Painless real upgrade without reinstalling

Upgrading a fresh Ubuntu x to Ubuntu x+1 doesn't give you the same system as installing directly a fresh x+1. This lead to having systems that are, at each release, a bit more far from the current release, with unexpected bugs that cannot be reproduced easily.

Ironically, most advanced Ubuntu users now reinstall their system every 6 months. And that was what we were laughing about Windows...

This spec adress this issue by proposing a real dist-upgrade mode which would allow you to fully upgrade your system, with more interactions than the simple dist-upgrade.

This spec doesn't not intend to provide the same "painless upgrade" functionnalities for beta-testers that are using pre-release. But it could be a nice side effect.