I've worked with several revision control systems. In the end, what they care about most is files. We have files, they're stored under the workspace directory.
Would it be sufficient to create a git repository, and shove the workspace in to it so that it can be managed using git's tools? Sure, it wouldn't be as pretty and nice as doing this in Designer itself, but would it work? If not, why not?
I think the basics of it might work.