This. And not just because gigantic team battle scenes are awesome. The X-Men have always been about "the team is greater than the sum of its parts". Just imagine this kind of a scene, with the X-Men: each member attacking, guarding, setting up, tanking, and flanking for the others. Cyclops at the center, blasting the enemies while trusting his teammates to protect him. Nightcrawler bamfing in and out, all over the battlefield. Phoenix shielding teammates, and tossing enemies into her allies' attacks. Colossus striding forth as an unstoppable force, gathering up all the enemies upon him.
Its what we should have.