From reading these Boggarts seem pretty unpopular and there is some question as to why two canine mythicals. Since we just got Leviathans too, we have a lot. So maybe in place of Boggart (and a canine one? though I like both of those) some sort of ghost-feline companion for a mythical?
They could probably be introduced in the new SWP--I don't know tons about it but it seems to involve new lands and mystery, the lil ghost cats could be discovered in a new land?
Sorry to break up the form but it was an idea I had after chatting and thought it was worth sharing.