OK, here are a few thoughts, after reading this thread, and making a few specific replies.
I think that combining
(1) Ryan's specific proposal in his previous message
...with...
(2) the cautions in my "just to be sure... so that... unconfirmed.surbl.org will get too convoluted and too bulky to be effective" previous message... (as well as keeping unconfirmed.surbl.org OUT of multi.surbl.org)
...will be a winner!
What do you think Jeff?