After GotG has established the "space" part of the MCU and
they could go for "planet hulk" (but with more Banner and a story that's a bit different)
8) he doesn't need to be, that's what makes him interesting
7) he probably wants to be the Hulk when he's on a planet full of things trying to kill him
6) in the comics the wormhole weakens him so he can be hurt
5) he might actively try to escape the planet and get back to earth
4) he can be a rage monster on the planet, or he could develop or it could be a split personality, it doesn't matter that much and none of it makes it a bad movie.
3) It would actually be interesting to see how the Banner and Hulk personas will work together to escape the planet.
2) Skaar, or maybe even a Guardians of the Galaxy character (like Drax or Groot) could appear. They even already have the effects for Korg, from Thor: the Dark World
1) If people like Guardians of the Galaxy, then this will probably work too