Phantom Forest question

It would only make sense for only versions with Masteria to get CK, since the versions with the event map of the Haunted Mansion don't have any backstory on Masteria at all.

That's not entirely true; CMS's event notice directly mentioned NLC, so whenever they do get it it's quite possible that they will get the mansion.

Or maybe there'll be a map after the HH map, or the HH spawn could be removed entirely from that map, or maybe it'll be like Showa where bosses spawn before you get in the town.

I suspect it'll be an entirely separate path, it would be far too cruel to make low levels have to risk passing Headless Horseman.