Before digging into specifics, I want to address a few issues that I think Marvel attractions face. First, I have a theory on what a Disney story requires and where it succeeds. Truly great Disney stories focus on yesterday, tomorrow, adventure, and fantasy. Disney does not do "today" well, meaning stories just about today with no magic, no other special twists. This extends to theme parks and their aesthetic as well. Disney California Adventure largely didn't succeed in its first incarnation because it contained a lot of modern buildings, which are frankly not exciting or welcoming for guests. Marvel attractions could suffer from the same issue. There are a couple of directions a Marvel land could go. Universal went with a "comics" accurate version with large cutouts and bold colors. It's an approach, but it's not very appealing. A Marvel Cinematic universe approach generally leads to a lot of modern New York style buildings. Only Asgard, Wakanda, and their outer space locations (Knowhere, Xandar, etc.) have any kind of interesting aesthetic. It then becomes imperative to develop a unique look and feel to the land.
Second, it is also necessary to make sure that one off attractions in current lands are added in a way that complements the park and does not clash with the established aesthetic. At least one particular current attraction implementation gives cause for concern. While Guardians of the Galaxy: Mission Breakout consistently ranks at the highest rated attraction at Disney California Adventure, the outside of the attraction is an eye sore that is visible throughout the park. While the previous attraction in this location (Twilight Zone: Tower of Terror) had similar sight-line issues, the Spanish Revival hotel style felt more appropriate in the park. The current attraction has an awful colorful refinery look that looks nice only at night because of an interesting lighting package. Hopefully, future additions will be more thoughtfully created.
Additionally, there is a concern regarding the particular presentation of the attractions given what Disney has done so far. The two Marvel rides that exist (Iron Man Experience and Guardians of the Galaxy: Mission Breakout) both have a heavy reliance on screens to create the characters that we identify with in the movie. For Guardians in particular, the cast filmed the scenes for the attraction around Guardians 2. This gives a continuity to the Cinematic Universe, but it can date the attraction very quickly. Screen based attractions in general become more date more quickly than other types of attractions. Additionally, it is important to have a well-rounded attraction style to keep the land from becoming repetitive. The focus of the best attractions is to create the experience that you would want from the movie or story that you remember. You want to fly with Peter Pan and Dumbo, you want to sail on a pirate ship, to blast off into orbit. The attractions for Marvel should do the same - they should allow you to experience the particular thrill of being that hero. To fly like the Falcon, to swing with Spidey, etc.
Finally, there are contractual constraints that tie Disney's hands in a lot of areas. When Marvel was going through bankruptcy in the early- to mid-1990s, they signed a lot of contracts that Disney is now regretting. For attractions, the primary issue is the contract with Universal and Marvel's presence in Universal's Islands of Adventure. This contract is a perpetual contract so long as a few minor requirements. It also has an exclusivity provision for all area east of the Mississippi with very few exceptions (meaning only certain Marvel characters can appear in Walt Disney World) and limitations on use of the Marvel name across the US (meaning Marvel land in California will likely be called Super Hero City or the like). This is the most challenging part of the Marvel situation.
With that, I will outline possible attractions I envision by franchise for Marvel properties, with suggestions for possible locations.
Agents of S.H.I.E.L.D. - The greatest appeal of Agents of S.H.I.E.L.D. is that they are the protective force anyone could join with the right training. Importantly, any attraction for S.H.I.E.L.D. should focus on that aspect. I can envision a Superhero Training Academy or an agent target practice ride a la Buzz Lightyear Astroblasters or Men in Black.
Agent Carter - I would love for Disney to dust off the old Dick Tracy Crime Stoppers plans and update them to an Agent Carter attraction. Would fit perfectly in a Hollywoodland or Sunset Boulevard - Disney Hollywood Studios section (and may be one of the few characters they could use there). It would be a rider through attraction where you get to use "tommy guns" to help take out the forces of Hydra, Leviathan, or the Zodiac. This could be a signature attraction.
Ant-Man & the Wasp - The experience of shrinking (and growing) leads to a couple of exciting possibilities. There are at least two extinct attractions that could be resurrected with new life breathed into them. First, Disney could add a new version of Adventures Through Innerspace, an omnimover attraction where the guests shrink down to the microscopic level and back. Now with Ant-man, it can be a journey into the Microverse. Second, a 4D theater attraction like Honey I Shrunk the Audience could be created to have the entire theater feel being picked up, hurricane force breath, etc. If nothing else, being able to explore giant versions of familiar objects is always fun. A Marvel Land, Tomorrowland, or even EPCOT would be a good location given the "science hero" aspect.
Black Panther - The desired experience for Black Panther is to visit Wakanda. That was such a fully realized, visually astounding place, that to be able to walk around in that land would be incredible. The attractions are almost secondary. I would, however, love to see a circle vision (or whole dome circle vision) attraction where you could feel immersed in the dream like quality of the "Realm of Kings." If a Wakandan land is built, it would be a perfect expansion of Adventureland. Further, an expo-like Wakandan Outreach Center would be a good fit for Tomorrowland or EPCOT.
Captain America - Captain America is one of the few heroes where the desired experience is to truly ride along with him on an adventure. Accordingly, an attraction for Cap would need to be a ride (with one fun exception). I could definitely see an Indiana Jones-like enhanced motion vehicle jeep ride along side Cap tracking down the Watchdogs, the Sons of the Serpent, Ultimatum, or Hydra. Likewise, I think the rumored Cap motorcycle darkride/coaster hybrid sounds amazing. These would be perfect for a Marvel land, whether at Disney California Adventure, Paris Studios, or Hong Kong Disneyland. For the one exception, I have long thought a Hollywood Canteen USO show would be a great addition to the golden age Hollywoodland. It would be perfect to have a Cap punching Hitler moment in this type of show.
Doctor Strange - Doctor Strange really needs to be a 4D theater attraction to allow for all of the truly trippy visuals that could be experienced. Particularly if projection mapping was used to allow the whole space to become part of the screen. I think you could even go with a form of a Magic Lamp Theater approach where you mix an actor performing stage magic and sleight-of-hand with the movie magic going on all around. It could be truly incredible. Plus, the Sanctum Santorum provides for great exterior architecture. This would need to go in a Marvel land, or perhaps the Paris Studios park or Tokyo DisneySea in the American Waterfront area.
Guardians of the Galaxy - Guardians surprisingly have the most flexible uses in the parks. Mission Breakout has proved this. The gantry lift drop ride has proved to be a very popular attraction. I also think the smartest re-theme of Star Tours is to Galaxy Tours. Think about it, you replace C3P0 with a Rocket animatronic as your pilot, with a potted Baby Groot on the dash, playing a new awesome mix soundtrack for the ride. You can visit Knowhere, Xandar, Ego, Hala, Sakar, and the like for variety in locations and can encounter the Chituari, the Skrulls, Ronan and the Kree, the Nova Corps, the Ravagers, and the Sovereign for antagonists. You could still keep the multiple ride profiles for repeatability. And thankfully, the Guardians can be used in Florida, so this could be rolled out at all Star Tours locations. (This would be a much better fit than the Guardians Energy ride in EPCOT). Likewise, I think Guardians would be a great re-theme of Stitch's Great Escape! Imagine if Groot was beamed down in the tube and needed to escape with the Novas or the Sovereign looking to study him. Less scary than Alien Encounter, but better than Stitch (anything is better than Stitch's Great Escape). The themes and setting of Guardians make them fit in any Marvel land and in Tomorrowland.
Hulk - Hulk is a difficult one because the experience that we would want as a Hulk is to be able to smash. Maybe with VR this could be accomplished, but the VR apparatus is better suited for Iron Man, as is discussed in the section below. His current attraction in Islands of Adventure is a roller coaster and I understand that choice (mega coaster for mega hero), but it really does not tie together. An attraction like Stitch's Great Escape! could work if it were a situation where Banner was captured and then busts out as the Hulk, but it could venture too close into making guests terrified of the Hulk (that could be an amazing moment though, if you could watch a Banner animatronic transform and Hulk out). Likely, the best solution is to use the Hulk in an Avengers ride only.
Iron Man - The desired experience is to wear the armor. To be able to fly, to shoot replusor blasts, to really feel like you are in the suit. I think the best way to accomplish this would be a VOID VR experience. It has currently been rolled out for a Star Wars experience and I think the two share many similarities. In the Star Wars version, your mission is to infiltrate a location dressed as a Stormtrooper. The Stormtrooper outfit provides an in story explanation for the equipment you have to wear for the VR. The armor would work the same way. Now, the experience is designed for around 4 people to work together and generally Iron Man is only one hero in armor (maybe two with War Machine), but this could be explained as a new prototype armor for all or as joining the Iron Legion. I think this could be incredible and a great addition for a Marvel Land, Tomorrowland or EPCOT.
Spider-man - The goal here is to swing. To feel that rush of swinging through New York city. The bounce and lift that would come with it. The ride at Islands of Adventure accomplishes this well, but focuses on a comics version, screen based view. The patent Disney has filed that arguably is for a future Spidey ride, I think would help accomplish this feeling, swinging side-to-side through the ride and allow for a more fully realized animatronic and set based attraction. Plus, it would appear to be a little more all-ages friendly. Very important for your neighborhood friendly Spider-man. Good for Marvel land or the American Waterfront in Tokyo.
Thor - With Thor, generally I feel the strongest connections are in the transportation across the Bifrost to Asgard and the land of Asgard itself. It's Marvel's Fantasyland. Without creating that space, I would have Thor included in an Avengers ride as well.
The Avengers - For an Avengers ride, I would want a mega-E-ticket that employs all the available technology, like LPS ride technology, projection mapping, many, many animatronics, physical sets, screens to extend the horizon, and every theatrical trick you can think of. This should be the big ride, like the Star Wars Battle attractions is going to be. Like Shanghai's Pirates ride. Animatronics of each of the Avengers fighting along side you to get you out. A giant Hulk animatronic you encounter. The team is protecting you as you get to safety. Marvel Land Anchor. It could be marvelous!
X-men - Planning for the Fox acquisition and total Marvel integration, the quintessential X-men experience is the Danger Room. Accordingly, an X-men attraction should be an interactive, immersive theater experience. Marvel land, maybe American Waterfront.
Fantastic Four - Likewise, the Fantastic Four signature experience is space travel and an encounter with the biggest threats possible. The Fantastic Four would likewise be a good fit for Star Tours, with a possible Armageddon style pre-show.
This does not even begin to include meet and greets and stunts shows, which any of the characters above could anchor, plus characters like Daredevil, Luke Cage, Iron Fist, Jessica Jones, etc. I would even love to see older, deeper cuts like the Two Gun Kid and Kid Colt as citizens of Frontierland.
This is all to say, Marvel has a bright future ahead of itself in Disney parks as well. I'm looking forward to seeing what Disney will roll out and hope to be amazed by what they can do.