8) Siryn
Played by Shauna Kain, Siryn made a cameo appearance in X2: X-Men United when her damaging sonic scream saw William Stryker’s men forced to take her down with a tranquillizer. She was saved by Colossus (another mutant making a cameo appearance here before taking on a much larger role in next year’s Deadpool movie), and showed up very briefly at the funeral of Professor X in X-Men: The Last Stand.
With a new timeline now in place, having Siryn show up in the next X-Men movie makes perfect sense. After all, her father played a key role in X-Men: First Class, so there’s some history there which could be expanded on in a future movie, especially as it’s believed that he was among those murdered by Bolivar Trask. Given her relationship with Deadpool in the comic books, Siryn showing up there instead could also work.