Honestly, if such a tool was to exist I would be really happy, because I've spent so many hours in my life repeating the same steps to make an idle animation, I'd happily let a machine do it. But till then, hand work it is. So if you ever make one, keep me updated :)
For now, I’m focusing on finding time to work on some neglected existing projects, preparing an initial release for a tool to streamline human-assisted OCRing of manga, and considering whether my plans for a tool to prepare tile atlases (as an assist for a platformer I want to code) should broaden into a free and open-source competitor to Pyxel Edit.
(But it definitely is an interesting UI design question… what controls would need to be exposed to an end-user to make it properly useful.)