Jean Grey has an excellent video game record. She could do incredible things in X-men: The Next Dimension, along with having her own Phoenix freakout in an alternate ending to the story mode and Dark Phoenix being a playable character. Jean appeared in Marvel Ultimate Alliance 2 and Marvel vs Capcom 3 during the dark years of her comic book death when it seemed like Marvel had every intention of keeping Jean in the past. Jean's TK was so fun in X-men Legends 2 - I loved powering up that move, picking up lackeys and throwing them around with ease (sometimes off ledges!)
Jean wasn't mentioned or hinted at in MUA3. Colossus and Cyclops had large NPC roles and they will be added to the game as free DLC. The X-men in the DLC pack could be anyone, but I think Jean has a great chance since she is popular and is a returning character to the franchise.