I've started collecting some notes on issues that need to be considered for a potential git migration:
http://www.mediawiki.org/wiki/Git_migration_issues
I'm paying particular attention to the localization workflow thing. Note that TranslateWiki's been working on StatusNet's git repository for some time; git itself isn't a particular problem. But changing the layout of repositories could indeed change how some things need to be done, and we need to make sure we know how to solve whichever problems come up.
I think it's pretty likely that we can work those problems out -- nothing's set in stone yet, and there's plenty of opportunity to experiment with some sample layouts first!
-- brion