What if Byrne hadn't left the Uncanny X-Men

 John Byrne recalls a classic era of the Uncanny X-Men: 

“See, thing was, altho Chris and I worked pretty well together, we were often at odds on who the characters were. As noted, until just a short time before I left the book, he had read no issues of X-MEN other than those produced during the Thomas/Adams run, and so, while I kept trying to maintain the characters as they had been for 60+ issues, he kept trying to turn them into other people. People I largely didn't like.

 And the problem was, no matter what I drew or scribbled in my margin notes, Chris would write the characters and the scenes as he felt moved to do when the pages where in front of him -- often completely changing my or even our original intent for a scene -- and THAT was what was seeing print. So, if the fans were loving the X-Men -- and it seemed they were! -- it was Chris' X-Men they were loving, not mine. I Chris had left instead of me, I very much doubt the book would have proved as popular as it did in the long run.”

Byrne’s last issue was Uncanny X-Men #143, but what if Byrne hadn’t left and stayed on to collaborate with Chris Claremont for a few more years. Well, here is Byrne’s scribbled notes:

Whether you’re a Claremont fan or a Byrne fan, it’s still intriguing to ask what if. It’s interesting to see how Byrne’s plan deviates near the end of the Dark Phoenix storyline. Retelling the story behind the original ending to the Dark Phoenix saga and Jim Shooter is in my queue. I can't help but wonder how they would have brought back the original X-Men team back into the fold.

Further down the list is the Sabretooth storyline which Byrne would have apparently revealed that Sabretooth and Wolverine were actually father and son.

From Fantagraphics' X-MEN COMPANION II (1982), Byrne revealed: 

"In my mind, [Sabretooth] was created [with the intention of making him Wolverine's father]. I don't think Chris originally conceived him that way, but I said, 'Hey, here's another Canadian guy who has a lot of the stuff, so I'll just draw him in such a way that he could be Wolverine's father -- or brother.' I wasn't sure in the early days. I figure Sabretooth is 120 years old.

As I dug around, I came across another tidbit in that Claremont and Cockrum had originally meant to have Wolverine be an evolved creation of the High Evolutionary. Also, apparently Len Wein, Wolverine’s creator had Wolverine at 18 years old and his claws were actually in his gloves and not coming out of his hands.