In the upcoming X-Men crossover event Extermination, we know that the X-Men face extinction 20 years in the future (what else is new?), and we know that it all has something to do with the original five time-displaced X-Men, but we don't know much more than that. Marvel has revealed the cover to Extermination #2 by Mark Brooks, however, and from that we can glean a pretty major detail: all five have been transformed into "hounds," the spiky-costumed mutant-hunters that originated in the Days of Future Past storyline, and which former hound Rachel Grey is still reckoning with in the pages of X-Men Gold today.
In an interview on Marvel.com, writer Ed Brisson (who teams with artist Pepe Larraz on the series) revealed in no uncertain terms that the 05 X-Men refusing to go back to their own time is to blame for this crossover debacle:
This series is about the Original Five—Jean, Bobby, Warren, Hank and Scott. Years ago, they were brought from the past to our present so that they could see how badly things went wrong with their older selves and, theoretically, fix it. They were only meant to be here briefly, but have stuck around for far, far too long and their presence is finally going to have some very serious consequences—not just for themselves and the X-Men, but for all of mutantkind.
Brisson also promised that the story will be steeped in X-Men continuity:
Our mandate going into this was, "Your back issues matter." Every single UNCANNY X-MEN story involving the Original Five X-Men matters. If the X-Men are here, then they're not where they're supposed to be, fighting those they're supposed to fight. What happens when that past starts to unravel? What's the butterfly effect on our present?
Look for Extermination in stores in August.