"This isn't a reboot." "It's like Pleasantville."
First, I've never seen Pleasantville so this might explain my confusion.
What I'm picturing based on descriptions is Jean (from the original X-Men team) in a Butterfly Effect-like moment gets a glimpse into the future (errr... NOW) and is dissatisfied with the way things turn out thus changing her actions and the course of events throughout the Marvel U. Yes? Wouldn't this create another timeline?
If it isn't the above then Jean zapping from that time into the present wouldn't make any sense whatsoever. That would mean that the Jean of the past was never there to experience all of the things from the past unless they use one of those "clever" clone stories to patch it up or better yet... a Jean from another alternate universe came in just as the real Jean beamed to the future.
Perhaps something else altogether? Please, comic community... I beg that you help me to comprehend this... this... ((HEAD EXPLODES))