For me the killer feature of this is the " you get diffs that can take you, in a single keystroke, to the very lines that were changed – loaded right there in your editor." Combined with branches being sandboxed had me extremely interested. Both of these have been a personal pain point/pinch point.
With that said, the mere mention of keybindings had me running for the hills (muscle memory, user training, etc.) In fairness they do end with "One hopes the idea is intriguing enough to encourage development elsewhere". While I'm not going to be the one picking up on that one, it has made me realize that the things I growl at about Github are experienced by others so yes, there is a market for something like this because up till the point of the keybindings I had my wallet open and was shouting 'here, take my money, I want this'