Well, I'm guessing the mod would delete anyone who signed up for treats who wasn't in the main exchange.

What I wasn't clear on, and the most recent post seems to maybe clarify, is I guess this is their way of our collecting/publicizing dear author letters? They must not be planning on making the signups public.

I've been in one exchange in the past where the mod was all "no, only one fic. No matter what" like, you can only "claim" on of your recipe's prompts and the rest were to be returned to them unwritten, basically. Fandom intellectual property norms or whatnot can go in interesting directions when people try to design things from the ground up instead of copying yuletide/kink-bingo/big bangs/etc.