(I am also trying to tell more people about the campaign so it has some chance of getting to the next stretch goal. That would be five other game designers writing character playbooks based on their own games, and I am fascinated to see what they would make.)
Riley listed said designers in an interview on Twitch, although I didn't catch all their names. One of the playbooks would be based on Armor Astir - my mom is much more familiar with that system than I am, and is very excited about that possibility.
I think the other game designers were Takuma Okada, Possible Worlds Games, Brandon Leon-Gambetta, and a fifth that I couldn't figure out the spelling for. I don't think I'm familiar with any of their work, but, again, interested in seeing what results.