I was just thinking, where in the timeline is Eris's world? The others are pretty close to the ATLA era, but Eris nor Kin has made any mention of it, so I was wondering if we should shake things up and do something really crazy, take advantage of these alternate worlds.

What if Avatar Kin replaces Roku as the Fire Nation Avatar? And the Air Nomads are alive and well? It's possible that Avatar Kin's devotion to the world could even avert the Hundred Year War -if, of course, that was even threatening this timeline. I don't know how different you want to make it, but just by replacing Kin with Roku, it could be very interesting...