As per:
https://lists.ubuntu.com/archives/ubuntu-devel/2012-October/036043.html
I'm still frantically putting the bits together for this, but it's now far enough along that I feel comfortable saying we're going to be doing it for Raring, so:
In the continuing cause of trying to make the development series more usable at all times, not just around milestones, I'm rearranging the way our uploads are processed. For Raring, all uploads will go to raring-proposed, and a modified instance of "britney" (the software that handles migration from Debian unstable to testing) will copy them to raring when they've been built everywhere and do not reduce the count of installable packages in the archive.
The intent of this is to come as close as possible to eliminating transient uninstallability problems in the development release. We probably won't get all the way there. It will still be possible for uninstallability to be introduced by copies not all happening in a single publisher run, transient uninstallability in -proposed will still affect package builds, and it won't catch all cases where sets of packages that used to be simultaneously installable stop being so (the general case of this is NP-complete anyway). Even with these limitations, though, it should make things a lot better.and
https://lists.ubuntu.com/archives/ubuntu-devel-announce/2012-October/000989.html
As I described in https://lists.ubuntu.com/archives/ubuntu-devel/2012-October/036043.html, all uploads to raring will now be automatically redirected to raring-proposed by default.
They will be automatically copied to raring once they pass various tests such as being no less installable than the previous version, and soon I hope to take autopkgtest results into consideration as well.
Attempts to copy ("sync") directly into raring will be refused. syncpackage's default will be changed in the next ubuntu-dev-tools upload, but in the meantime please use 'syncpackage -r raring-proposed'.
This was one of the last blockers to opening raring for general development, so we should be able to get moving on this fairly soon. Cheers,