Re: MCU Phase 3: Have it your way
If they absolutely had to adapt Planet Hulk, I say they should ditch the betrayal angle entirely. Have it be some villain who sent him off into space, and have Banner/Hulk *know* this from the getgo. That would still work fine for stranding the Hulk on an alien planet, and forcing him to make his way there.
I think its unlikely on a budgetary level, though: you'd need the Hulk on screen for some absurd percentage of the film, and without the prospect of Transformers-level gross, I can't see that being approved. Whereas a more ordinary Hulk 2 can split time more readily between Hulk and Banner, which seeing as Ruffalo's Banner was a big part of what made the character appeal in Avengers, is a win-win.