Nonmod Matt here with a few characters, one definitely and a few maybes.

Caleb Widogast the disaster wizard hobo from Critical Role is coming - but it's the one from 15strangers, so he's from episode 2x58 and also heavily traumatized. He also comes with a spoiler warning for both Fallen London (specifically the Seeking sidequest) and Mystic Messenger (to a lesser degree), so let me know if you're not okay with spoilers for that.

Other possibilites include Casper's future adopted kid (again) and my Changeling character who popped out of Arcadia a hundred years after she was taken.