There is a conveniently large empty area smack in the middle of this PCB, and it makes me have ideas. The most obvious one is to put a display there — then not only I can see any messages or exceptions from the CircuitPython code running on it, but I can also display things. Or, like, have menus and settings. A library of Unicode characters and emoticons. Fancy animations. Sky is the limit. But then I would probably also want an external flash storage and a SAMD51 microcontroller with more memory, so I guess I will not do that.
Another thing I could put there is something that would let me not have to take my hand off the keyboard to move the mouse. A trackball, for example. Or a touchpad. Or, you know, one of those cheap tiny joysticks they use in handheld consoles. That seems like a reasonable idea, and I can always simply not populate those footprints if I change my mind.
I also added a pair of tact switches on both sides, for the mouse buttons. Still tempted to add an encoder wheel with a third button, but I only have the kind that is mounted flat on the edge of the PCB, and that doesn't work with this design.
I'm still considering adding a few LEDs on the free pins, for things like CapsLock or layer switching indicators.
I'm also closer to actually ordering the board and the switches, especially with the utter failure of the #Turbot Keyboard project, since that means I actually *need* this keyboard.