This is apparentally this Summer's big X-men storyline, while the other MU will mainly deal with Fear Itself. It seems to be a bit deriative of Civil War-basically, Wolverine and Cyclops form opposite teams of X-men: One with Magneto's philosophy, the other with Xavier's. Allegedly this will bring X-men to a tighter continuity with the rest of the Marvel Universe as well.
It also seems that the storyline will bring back an important character from Morrison's run. They've used Sublime too recently, Xorn is a continuity nightmare, and many of the students have joined the new mutants or something...so who?
It also seems that the storyline will bring back an important character from Morrison's run. They've used Sublime too recently, Xorn is a continuity nightmare, and many of the students have joined the new mutants or something...so who?