I think one of the retcons that Hickman made that is hardest for me to fully grasp is that Prof. X has had Krakoa in mind from the get-go. What, are we meant to think, he was waiting for? And did he know what was going to happen throughout all of the stories? Did he know Jean would be Phoenix? Did he know about Wanda? Genosha? How complicit was he in everything that has happened throughout continuity. How much of Moira's 4th life (the one that refers to the Phoenix Five as the Lost Decade) did Xavier get access to?
What did he think of the Utopia era? Was that not basically his vision? Why did he reject Magneto when he came to Utopia? What exactly triggered the decision, post Rosenberg's X-Men, to enact the Krakoa plan? I think the Moira retcon works, you have to make some things work to have it totally track but I think you can do it. The idea that Xavier knew what was going to happen to mutant kind but still allowed it all to happen is harder to make fit.
For that matter why did Magneto attack Cape Canaveral in X-Men #1? We know in HoxPox Moira's diaries mention "losing" Magneto and this seems to refer to X-Men Vol. 2 1-3. But did they not "lose" Magneto before that? In the Silver Age? Is that why Moira tried to warp Magneto's mind when she aged him up from a baby? What exactly was the deal that Professor X, Moira, and Magneto make in HoxPox entail?