Now that the new Krakoa X-Men have been revealed and both Polaris and Rogue most likely will leave their current books, let just do this for fun.
Who should replace Polaris on X-Factor and who should replace Rogue on Excalibur.
It has to be a mutant (of course) and not a member of another current X-book.
Personally I would like to see Hellion enter Excalibur and Surge to enter X-Factor. Time for those former New X-Men to get an upgrade.