Gitocello [1] takes this approach. While Tim Felgentreff started it to ease porting between Squeak and GNU Smalltalk, it works just fine as a new MC backend. I use it a fair bit [2][3][4].
Mind you I _haven't_ tried collaboration with it. If you had conflicts you would need to use git to address the conflicts, and you can have "inter-method" conflicts which are impossible with FileTree. (In other words, conflict markers could start in one method and end in another.) Probably the chunk format's date stuff would get annoying, as well.
[1] https://github.com/timfel/gitocello [2] https://github.com/frankshearar/Unification [3] https://github.com/frankshearar/PersistentUnionFind [4] https://github.com/frankshearar/Zippers
frank
ah nice, though you went for the one file per class approach. Which I think is not the best solution for pharo. For instance I want to replace the .changes / .sources file with one git repository which allows you to simply load new changes on demand and find methods with a minimal effort :)