Just my theory but considering the story moves through the seasons and the school year too given it's structure, my likely guesses for who are the next three girls would either be kitty pryde, storm and either emma frost or jubilee.
Why? well given that the main character would be in his second year by the time v0.4 comes out, storm is likely to appear since she's already teaching there and story wise, it's only in the second year that the MC encounters her due to her teaching one of his new subjects (probably). As for kitty pryde, it would just be interesting to have her be a first year student and you the MC, being a second year, showing her the ropes in the school, just a different dynamic compared to the first three girls. (btw, I'm not sure if kitty pryde is already in the game either mentioned or as a cameo so I may be wrong, it's been a while since i last played). I say emma frost or Jubilee because emma adds another teacher character to the game and it's jubilee, she's another popular xmen character so why not?
This is just my wild and probably shit prediction, for all I know we could get wild cards like polaris, magik, mystique or even scarlet witch, who knows? Fuck, for all we know it might even be kurt in the next update xD
