Alright, the PR is up - Add brush tip rotate actions (!1967) · Merge requests · Graphics / Krita · GitLab
On the UX side, I ended up adding 4 actions (hotkeys), to rotate the brush either quickly (by 15 degrees) or precisely (by 1 degree). It works for the Krita brushes (pixel engine) and MyPaint. There are some niche engines that I left out, but these don’t seem to benefit from the rotation too much, if at all.