First of all: Thank you! I am really interested in trying your firmware. I have done some work on the stock firmware myself lately and have grown just a little bit tired of flashing 
As external connectivity is very important to me, I wanted to ask how your version handles plugging in external USB devices before I give it a go. Does the keyboard stay in DFU mode after voltage dips?
Edit: The web-based tester is really cool! Just a little heads up: At least for me, the game buttons register slightly swapped. Y registers as Y, but B registers as X, X registers as A and A registers as B.
Edit 2: This “bug” only applies to the stock firmware. I just flashed your version and it feels great! Also: Connecting USB devices works!