Can we expect to see an updated package for GDC in the Ubuntu 12.10 repositories some time soon?  (Ideally for 12.04 as well, but I don't know if that's permitted under Ubuntu update restrictions.)

It's currently still on 4.6.3, which is some way behind current DMD and upstream GDC:
https://launchpad.net/ubuntu/quantal/+package/gdc

It would be better still if we could have a PPA with latest GDC available for all the currently-supported Ubuntu and Debian variants.

Asking for this is purely down to laziness and stupidity on my own part (I screwed up trying to build GDC from source and haven't put in the time or mental energy needed to work out what went wrong and fix it), but since if you don't ask, you don't get, I'm asking. :-)