Ha, a fellow Krit...ter...er?
Yeah, Krita is awesome! it merges all the nice brushes and functions from MyPaint, Alchemy, Gimp, and adds a lot of its own. Fell in love with this software quite a while ago.
I wanted to get some hardware specifically for Krita - I use a convertible laptop and I'm often drawing on the run. The most comfy way to use it is to have it flipped with the keyboard outwards, so it acts a bit like an easel, with screen close to you, positioned at an angle. But that makes it impossible to use the keyboard, so I have to keep the application interface visible most of the time.
I was pondering building a controller specifically for Krita. Though what you're writing makes it quite worrisome.
I'll have to look into it, if it has some sort of an API that can be used. Or hook up to the vars directly in memory, and change them with an external process... but that would be really hacky and possibly unstable.
Did you talk to the devs about it?
Getting a similar thing for Blender is really easy, you can call every variable in the app with arduino and pyserial, and it works both ways.