That being said, I have a Monoprice tablet I use through libinput. I used the wacom driver for a bit but libinput gives me enough to do what I want (I have to say having to do matrix math to constrain the screen size so the tablet is in 1 to 1 correlation to the screen was a bit rough on the UX front). Libinput is pretty feature complete on tablet support in the basic use cases, it is just missing a bunch of the tunables from xsetwacom. The Digimend project has done an amazing job providing driver support for a lot of non-wacom tablets as well. It will be interesting if its Wacom tablets that are the pain point on Wayland. I don't have or know anyone with one to confirm or deny if the libinput support is up to par.

If I had the confidence to know what I'm doing (and I don't, I've never touched the Kwin / Wayland / input stacks on Linux at all) I'd try wiring in tablets to Kwin, but you probably want that first - which is still at least a release or two out at best - before you even think about trying to port your KDE Painting app to Wayland.

Why not provide a --no-tablets-i-just-want-wayland option that would not force the X backend?

So turns out it's easy to turn off X11 in the build files https://github.com/myfreeweb/krita-wayland/commit/8ab43e3e1c... and it does work on Wayland now!