>Whatever benefit you think this is going to bring when it's done, why not prototype that now?

The biggest benefit is removing the need for a configured, physically accesible, machine in order to do your work.

Imagine visiting the parents for a weekend and being able to fix a small but urgent bug and do a commit using either something you have with you (like your webkit-based device) or what they have there (low-powered machine). Using a browser seems the most natural.