X-Men DOFP was like a potluck. Everyone was invited, and they each brought something to the table, no matter how small.
Lucas Till's HAvok played a minor role, Lin the military, introduced along with Toad and Ink. No word if they will be returning, but we know someone will:
HAVOK! Brian Singer recently confirmed that he will be returning. He, along with Beast, are the only Division X members who are (most likely) still on Xavier's side.
Just like in First Class, Charles Xavier's recruits will be teens: Cyclops (Tye Sheridan), Storm (Alexandra Shipp), Nightcrawler (Kodi Smitt-McPhee), Jubilee (Lana Condor), Jean Grey (Sophie Turner), and Angel/Archangel (Ben Hardy)
They will probably be students who are "seniors", and rise to fight The Hourseman and Apocalypse.
In the comics, Scott (Cyclops) and Alex (Havok) are brothers, but given the major age difference, could they be FATHER/SON?
Maybe Havok could be a teacher, because he has had his powers for a while, and was a original member of "Division" X.
Given his military allegiance in DOFP, he could have been captured as one of the Four Horseman, or working with Moira MacTaggert or William Stryker(?) for the government
However he appears, we know it will be nothing short of AWESOME!
Singer also posted a photo of him scoping out fillming locations, indicating it will start in a couple weeks