Voting starts in March for the Drupal Association Board election.
I'm starting to play with uc_addresses... so far, it looks like it does what I need -- thanks!
One minor UI/UX improvement would be to use drupal_set_destination() when we link from the cart checkout page for users to edit their stored addresses. That way, after they update their address, they're automatically redirected back to the checkout page again...
Patch coming soon, stay tuned.