I pushed through with some of the changes I was making on monday, and implemented a mechanism for provision to conditionally include version specific code. What this means, is that 1 checkout of provision, will now have all the information it needs to manage any supported version of Drupal you throw at it.
Additionally, I created the 'deploy' command, which allows you to publish a previously created site package (aka: aegir backup), and roll it out under a different name on any platform. The deploy process will also run the 'update.php' code once a site has been deployed on it, so you could re-deploy mylivesite.com onto d6.mylivesite.com to provide a test base for the upgrade.
In addition, I added the migrate command, which automates the process of creating a backup of the site, deploying it on another platform, and deleting the site from the current platform (if all goes well).
What this means, is that aegir can now do major and minor version upgrades. HOWEVER: this is definitely not production ready. There is currently no dependency checking being done, so provision will not throw an error if you try to move an acquia carbon install profile site to a standard Drupal platform, without the modules or install profile available.
I wrote a very simple contrib module, which adds the migrate task for upgrading, but this will only work on 0.2 based platforms (ie: if it has hostslave and the provision module, it will fail. because hosting currently depends on the provision module, your main hostmaster platform will not be able to migrate sites quite yet).
But enough about that, how about some pictures :
