Kid Omega's not in the fight (though I hope he will be eventually since he can now make psychic shotguns on top of his other abilities), and some of the X-Men are sided with the Avengers. Wolverine and Beast I saw in the carrier, so I'm sure there are others like Iceman or Rachel Summers (a previous host of the Phoenix) will side with the Avengers as well. There's actually a surprisingly large amount of mutants unaccounted for in this event, so far. Of the remaining 200 mutants, less than 100 are actually in Utopia.
What I'm most curious about is....where is Professor Xavier during all of this? If this ends with him returning as the rightful leader of the X-Men, and laying the smackdown on Scott, I will jump for joy.