Provide a PPA mechanism to delay publishing binaries until all architectures are built

With multiarch now available in Ubuntu, it becomes increasingly likely that users will have different arch versions of various packages. This can create a problem if they are using PPAs, as the archive skew can be considerable - one arch may build many hours before another.

If a user of the PPA updates during this window, apt may select resolutions that remove packages which haven't built as fast, since multiarch packages have implicit depends on the same binary version.

One solution to this is to build packages in a staging PPA and then copy all arches simultaneously to the real PPA.

This isn't really a solution, however, for automated builds such as daily recipe builds, and it's an additional burden to the release process in normal PPAs as you then have to monitor launchpad to see when all builds complete.

What I want is a way out of this mess. Maybe launchpad could automate the staging PPA -> copy to real PPA if all builds complete successfully process. Maybe there could be a checkbox that would forcefully prevent this archive skew in the PPA settings somewhere - launchpad would withhold publishing the package until builds for other arches complete.

If builds fail for some, but not all, arches, I'm not sure what to do. Publishing as normal in staging but not "real" would be nice, if the automated multiple-PPAs solution were done.