I am very interested in the Overlay Creator. I am a programmer and I've glanced through the API and that seems doable but requiring more time than I have at the moment. I'm just interested in taking the standard piano keyboard that you have and creating an overlay that uses a completely different keyboard layout.
If I went the API route, I would need to rebuild all the existing pressure-to-MIDI conversions that you are obviously already doing, so the Overlay Creator sounds like a much better fit.
Please add me to the Beta list as well.