OK, thanks. I probably won't go much further, though. Since the input is (tried to be) read from Linux input devices (/dev/input/...) and not from Xorg or the console, I'm not surprised that software keyboards do not work. That would probably need a more sensible drop-in specifically addressing the touch input. I'm lacking a test device (and before you collect to get me one, read the following
and the time/devotion to do this myself.
Even the K4 will need some adaption w/ regard to key codes, I think. This should be more simple in comparison, but again that isn't a job for me, sorry.