Why Marvel Need To Make An Avengers Vs X-Men Movie
Opening The Multiverse
The best approach to bringing a fully formed (or at least partly formed X-Men team to the MCU) would be to have them arrive from another version of Earth in the multiverse (which has now all but been confirmed by Ant-Man and Doctor Strange). We know some form of dimensional travel is possible, so why not leaping between alternate versions of Earth's reality?
It's something that has happened in the comics a lot - particularly when writers are faced with deaths or undoing major fallout from event stories - and there's no reason why it couldn't happen in the MCU.
That way, we could have a ready made excuse for why there aren't any mutants (or at least no mutant superheroes) in the MCU. They've just not got to that point without the stimulus of a rising villain like Magneto intent on crowning them the superior race.
Mistaken Identity
When the X-Men arrive, the inevitable reaction of the world's governments would be anxiety and paranoia. They've already just seen invasions of Chitauri, Thanos' Black Order and presumably the Skrull army and having any unknown threat suddenly appear out of nowhere isn't going to make anyone feel comfortable (particularly with the Avengers weakened, presumably).
Their response would be inevitable: sending the new Avengers (now isolated from the Guardians Of The Galaxy) to investigate and defend Earth from these new, strange creatures (who would inevitably be classified as a threat). Cue several large scale encounters as the Avengers try and overcome their perceived enemies, who react to defend themselves.
Neither knows what the other team's intentions are - they're from entirely different worlds, after all, and there's precedent for both to suggest there could be legitimate danger. So they fight, and audiences everywhere are overcome with the sheer thrills.
Galactus Rises
The question of what sort of thing would drive the alternate universe X-Men to leave their own dimension is a tricky one, but there's one giant purple excuse waiting in the wings.
What if the alternate version of Earth was destroyed by Galactus, devourer of worlds, who has set his crosshairs on eradicating every version of Earth? What if the inter-dimensional travellers jumped through a wormhole/rift to warn their otherworld counterparts and help them defend themselves against a threat they'd already seen win in their dimension?
That would allow for a resolution of the initial conflict between X-Men and Avengers and a means to build to a second crossover film with the impending arrival of Galactus (assuming Marvel want to follow Thanos' two-part saga with something similar).
It would certainly be a great way to make the two teams allies.
Would you like to see an Avengers vs X-Men movie? Share your reactions below in the comments thread.