I agree the Xbox brand should stand separate of Windows overall. The author did show an image of the Xbox + Kinekt at the beginning but focused on showing the new branding on a laptop later. Perhaps he simply ran out of time or thought it would be obvious that the same branding would be used?
The Xbox user interface has been changing to look similar to the new "Windows 8 style" recently. I think you could easily take one of the proposed "Slate" images, duplicate and flip it, then overlay it over the original to make an "X" shape. That would create a nice fresh brand image for the next generation of xbox's and fit in with the proposed brand redesign as a whole.
Using Chrome on the mac, the "New Project" shortcut open a private browsing window. I believe the browser shortcut issues are being addressed already though.
Overall I like the idea a lot, I've just began learning how to use VIM and this app seems a nice way to learn, but as has already been mentioned it seems more like a practise tool rather than actual teaching. The only way to learn the answer is by getting it wrong the first time. I think there needs to be more focus on the "shortcuts" tab, or at least integrate together with the main app.
I believe the concept is to compress the logic into 140 bytes or less, not the whole application, the initialisation code is for "free".
My favourite part of these experiments is watching the gist comments, it's fascinating to see just how many bytes can be crushed from already tiny code, with a bit of help.
I can see myself doing something similar one day, so I have sent an e-mail over hoping that we can talk further.