A couple of news. First, I changed the layout again, to bring it more in-line with the Planck-like layout I use on my main keyboard now:
I moved the arrow keys to a layer and added a second layer switching key. Also, the Fx keys, when pressed with that second key, work as Alt+Fx instead of Shift+Fx, as that is more common for them.
Second, I got some simple animations going:
And finally, I cleaned up the code a bit, added support for any number of layers and for media keys, and released the code as a library at GitHub - deshipu/ukeeb
There is no documentation yet, but I included the examples from my keyboards. The code is small enough to run on CircuitPython on SAMD21 without external flash.