The studio is keeping quiet on the finer points, but it's unlikely that it will revolve around the teenage versions of Cyclops & Co, as the series X-Men: First Class actually does. Instead, they'll be using the young X-wannabes introduced in the previous three films, like Iceman, Angel, Rogue, Kitty Pryde, Jubilee (if you can call her cameo an introduction), and Colossus. I'd love it if they kept it current to the comics by mixing some of the Astonishing students, like Blindfold and Armor in -- especially if Armor replaced Jubilee.
It's inevitable that several of the young X-Men will be recast, as I don't see Ellen Page, Ben Foster, or Anna Paquin returning, though Shawn Ashmore might. There's also hints that Fox might recast some of the established X-Men in order to keep them around -- but given who was left standing at X3, that amounts to Beast and Storm, because you know Hugh Jackman would be willing to pop his claws in a scene or two. (Oh, my geek heart would soar if they would take his friendship with Kitty Pryde and run with it!) While I know this has the potential to be teen fluff, I'm actually pretty excited by this. The X-Men will always be my favorite superhero team, and I'll take a new class if it means seeing them on the screen again. I won't take The O.C. with mutant powers, though, so let's hope this is done relatively classy.