Another thing to consider is yes while marvel is owned by the Disney company, it is not owned by disneyparks. So the company is still very much acting in an independent way just under the Disney umbrella. Take for example the movies.... Marvel is linked to x men and spiderman but those are not Disney films they are fox and don't respectively. They do not refuse to allow those films to happen, so I would assume an expansion would work in the same way so long as the characters used in the expansion fall under the terms of their agreement. Keep in mind captain America and thor appear in the island but not in attraction form so I would assume since they do appear, a ride based off their character would be plausible.