Interesting, I didn't think you were serious when we discussed it earlier;)
Not that I'm against it, but it does have one downside which is that HEAD can no longer be treated as a development playing ground between releases (people can just make new branches though) and on the up side we'll no longer have to backport stuff that needs to go live on wikimedia sites earlier than the next stable release to what is supposed to be a bugfix-only branch.
Good news.