Well, it's telling if you're properly read up on your '80s X-Men storylines.
Speaking to IGN, X-Men series producer Bryan Singer has confirmed that the next chapter of Matthew Vaughn's mutant reboot will be subtitled "Days of Future Past," and furthermore claimed it will draw from the famous comics arc of the same name.
For those who haven't yet caught up on their early 1981 Uncanny X-Men issues, the Days of Future Past storyline involves a future in which the assassination of Senator Robert Kelly has created a police state dystopia in which sentinels keep all our favorite mutants locked down in internment camps. To try and stop this future from happening, Kitty Pryde's mind is sent into the past to warn of it; though she succeeds in her task, her alternate, shitty future continues to exist as an alternate timeline, and that's how the X-Men teach us about time travel.
Pressed if these time-bending, alternate-future aspects of the story could mean a tying together of Vaughn's '60s-set X-Men films and the modern-set films Singer (and, of course, Brett Ratner) previously directed--because isn't it about time we gave Patrick Stewart another shot at bridging a geeky series' generational gap?--Singer was cagey in his response, but did say:
"It's time to reach out and explore it and perhaps bring some connectivity between the films as Marvel has done so well. So, you may see some of that, I don't know."
Beyond its sci-fi tinged story, Days of Future Past is equally famous for John Byrne's above cover, which has been countlessly imitated and parodied since its release. So, needless to say, if there does end up being some X-Men generational cross-over, I am pretty excited for a studio-made, sloppily-Photoshopped simulacrum of that image to give us formal notice that Kelsey Grammer has been slain.
(Thanks, son_of_bokonon. Turns out you were right.)