Everything is leading up to the movie. Mordecai will join Anti-Pops for some reason in one of the final 4 episodes, Mordecai and Rigby will fight and one or both of them will die, something will happen to undo it.
Or they'll try to make a twist and it's Rigby who joins Anti-Pops. It seems like they'd never join the bad guy but Future Mordecai damn well knew Ross' intentions and did it anyway. He helped kill everyone at the park, was all for fucking up history's timeline, and was probably sucking Ross' dick in his spare time.
The only evidence that suggests things won't turn out the same is Future Mordecai's speech to Present Mordecai about how he sold himself out, had no friends and no family (probably killed them too but they didn't elaborate, he might've just cut ties), and that he climbed the evil corporate ladder for nothing, which made Present Mordecai even less to join a dark side.
Still though, it'd be interesting to see because they even placed the Space Tree from this season in the background of the movie and never once mentioned it, and no one in the space tree showed up, so it's like the timeline is completely falling into place.