This, seriously.

The backend could be git on an SSH server, but if you have a slick design and 100% operational uptime-- you'll capture 80% of the developers using Github currently.

I think that's incredibly optimistic to the point of unrealism.

Github, outages and all, is a known commodity with a reputation they can make money off of.

Any replacement would have to offer not just compelling feature improvements and uptime, but to have a history long enough to make it trustworthy to migrate to.

And uptime? Easy when you have a small number of customers. Much, much more difficult at a million+ customers (although Microsoft has really dropped the ball).