All characters mentioned in this synopsis are property of Marvel, this is simply fiction for fun.
I have faith in Bryan Singer, I do, but this is gonna be a tough one. Ratner and the writers made a pretty big mess of X3 and pretty much eliminated the possibility of Rachel Summers existing. Without her, we have to find another gateway to the past...AND without Kitty even being born in the 70s (since that is the supposed decade we'll be be set in) she wouldn't have a younger self to transfer her future consciousness into anyway.
SO, I propose this....doing everything within my power, within reason and in consideration of the masses who don't know the X-ins and X-outs while still easter egging the crap out of you guys ;)
In the future timeline, we have Storm, Colossus, Kitty, Iceman, Nightcrawler....and Illyana imprisoned. After hearing the dying words of an elderly psychic woman named Irene (or maybe even Emma Frost) about a man named Essex who tampered with mutant DNA to create the Phoenix which ultimately lead to their future, the future X-Men devise an escape plan involving Illyana's newly developed time-travel portals. Obviously, things don't go according to plan. Storm is killed creating a diversion and Illyana is captured while the others make it through.
The quartet of mutants emerge in the 70s (I'm reading up on my history of New York in the 70s, they don't exactly have to arrive at a pivotal moment in history, but the historical references need to be poignant and accurate...aside from, y'know, the existence of mutants)
SOOOO Fist class left us with a wheelchair bound Xavier with a full head of hair, blue, furry Beast, Havok and Banshee....who were honestly kinda "meh" characters for me in the movie. I think if they went with a Mr. Sinister storyline, Havok would actually be pretty important (and also in this continuity's concept of time, is it more likely that he's Cyclops's father rather than his brother?) Anywho, the future X-Men seek out Xavier and his X-Men, encountering young new recruits, Storm and Douglas Ramsey (shhhhhh, I think he'd work well here)
Once Xavier accepts their proposition to find Essex, they first seek out a legendary mutant that evaded all attempts of capture by the Sentinels, Wolverine (of course) SO the lineup is Wolverine, Havok, young Storm, future Colossus, Kitty, Iceman and Nightcrawler and Beast and Cypher (the latter two of whom just fly the plane or coordinate communications, have intellectual banter and act awkward around girls (also, I'd kinda like Cypher to represent a different ethnicity, maybe latino and his last name could change to Ramirez. What?)) With such a large cast, I kinda want Banshee to go bye-bye AND I think there has to be a cameo of Dazzler, maybe even just a poster promoting her concert or a news report outing her as a mutant or something)
Back to the skeleton plot I'm randomly assembling: Back to the Future ;) The heads of the internment camps bring Illyana to the cells where they hold the most dangerous mutants...because it makes sense to keep all the most dangerous mutants in one place, together ;). We see some cameos here, Franklin Richards, Scarlet Witch, Proteus, Mister X (it doesn't really matter who, just some powerful mofos)....and then there's Xavier & Magneto, who'll be super old. And here's the deal, the main guy, Bastion, doesn't like having to report missing mutants to the higher ups, so he introduces Nimrod and forces Xavier to telepathically force Illyana to teleport Nimrod to exact time and place she did her teammates so they can be bagged, tagged and brought back to the future (I love typing "Back to the future" teehee) But since the portal is forced and Illyana is so inexperienced (and since Xavier is a bad mama-jama), things spin out of control, releasing several mutants, Mags and the Prof included, who snag Illyana and jump in the portal after Nimrod. By the time they stumble out of the portal in the past, Nimrod is gone and, yet again, Illyana doesn't make it through with them (It'd probably be too much for a non-comic fan audience to digest, but I'd like to later explore Belasco abducting her mid-transport....and then dive into Inferno in the 3rd installment in the 80s with Sinister's clone of a prepubescent Jean, rapidly aged to adulthood, Madelyne Pryor....if that's too much of a stretch, she just doesn't make it because she's never teleported to the past before)
....Not sure where to go from there, I'll be back