5. Emma Watson - Jean Grey
It is inevitable that Jean Grey will return to the new X-Men timeline at some point, given how important she is to the formative years of the X-Men, and Bryan Singer has already dropped hints that he will recast the key X-Men characters who haven't yet been redone by the new timeline started by First Class. If we're going to see a version of the Apocalypse story arc where Cable does appear and take on the Godlike mutant, inevitably we're going to have to see the lead up to why Cable is such a key to his demise. He is of course the genetically superior offspring of Grey and Cyclops, and as such both of his parents are going to need to appear - perhaps as the key to why Apocalypse chooses to go after the mutants in the 1980s. Perhaps we could see Apocalypse appear under the guise of raising mutantkind as the dominant species, only for the X-Men to discover that his real agenda is to wipe out the chances of Cyclops and Jean Grey conceiving Cable, and ensuring his future demise never happens. Watson might have taken a while to cut her teeth in the Harry Potter franchise, but her subsequent work has been a lot more impressive, and she has similar poise on screen to Famke Janssen, and importantly she is more than capable of showing the slightest hint of darker waters beneath the surface that would make Grey the complex character she needs to be.