WordPress is a community driven project. If you want a feature, write it. The same goes for this -- if someone wants a legacy branch, then they should step up and volunteer to port patches to their older version of WordPress. I think it's being selfish and asking to much to expect that the already busy core devs maintain multiple versions of WordPress.

@Dougal Campbell - I don't see the need for more people with commit access rather than having them just submit patches and poking a committer for them to commit it.