Who knows, maybe GIMP will jump straight to Gtk4.
There's a good roundup of happenings in 2017 in GIMP here:
https://www.gimp.org/news/2017/12/31/gimp-and-gegl-in-2017/
[EDIT] There are links in the above doc to sponsor GEGL developers [/EDIT]
It's encouraging that GEGL is seeing use in other projects and receiving patches, maybe the GEGLisation isn't too far from completion.
We are simply not in a position to do centralized crowdfunding.
meanwhile Krita: "We can probably postpone worrying about Wayland on Linux for another year" https://krita.org/en/about/krita-roadmap-2017-2019/ >_<
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!
Remember Gimp --> GTK? And Gimp is still limping on Gtk2 and blurry on each and every scaled Wayland installation.