Couple of things, repos can get pretty big, how are you planning on storing things? Using the HTML5 storage? Kicking it down the drive? If it's with HTML5 storage after that guy found a work around allowing sites to completely burn through a drive browser devs might start putting a cap onto the limit of storage that you can use.
I don't know, I'm a big fan of getting tools to everyone, but I'm still wondering if this sounds like a great idea, without actually being a great idea.
EDIT: that last line might be a little overly harsh looking back on it, it's not that I don't think it's a good idea (definitely is!) but I'm wondering if it's a great idea that's worthy of a Kickstarter.