Comment 3 for bug 508525

For what it's worth Bazaar supports the Mercurial, Subversion and Git file formats through plugins - it already has an abstraction layer. The Git and Subversion working tree support is quite decent, support for Mercurial working trees is still pretty limited at the moment.

I.e. if you install bzr-hg and add --format=hg to the "bzr init" call this should ideally work already.