I'd argue Marvel in Tomorrowland is a better fit than many would imagine and could actually help unify the current disjointed land. I think it comes down to the roots of each. Tomorrowland, at it's roots, is 1950s/1960s near future sci-fi. Marvel Comics, in their heyday and in the form of the heroes most known, is 1960s sci-fi and science heroes at that. Marvel science heroes in a 1950s/1960s near future sci-fi kinda works. And with just a light retheming in many places. Ant-Man and Dr. Pym for Honey I Shrunk the Audience. Galaxy Tours instead of Star Tours. Stark Expo in Innoventions, perhaps taking the bottom floor and something else on the top, like the Space 220 restaurant at WDW. Captain Marvel and innovative space travel in Space Mountain. SHEILD training instead of Jedi training. And so on. I think it would have captured the land and given it a specific feel in the same way Indiana Jones helped solidify Adventureland.
Instead of trading and putting Galaxy's Edge in DCA, I always wonder what would have happened with Marvel and Star Wars both in Disneyland drawing crowds to separate ends of the park, and the space in DCA becoming nearly fully PIXAR (instead of PIXAR Pier). Bug's Land stays. The expansion pad becomes a Toy Story Land. Hollywoodland becomes PIXAR Studios.
It's that combination that I think would have made both parks stronger.