Most of the transfors you describe are still unfortunately destructive (ie the only way to go back is to undo). I'm not an expert on this, but I think the only way this could be key framed would be to take snapshots of the pixels and insert the modified raster data as keyframes? I'm not sure there's a good/correct/obviously way to interpolate betweens say a before and after liquefy operation the way it currently works. Maybe some of them coul store brush+inputs (pressure, cursor movement, etc) but that seems difficult to work with as an artist. Again, not done much animation (as a dev or artist) so maybe I'm just out of the loop completely

But yeah I agree with you in principle though, it would be nice if these were non-destructive and could be keyframed.

They are all non-destructive in Krita. Just use a transform mask and go to tool options, select liquefy and after you liquefy however you want you can just hide the transform mask and it stops liquefying the layer.

Yes, Krita has had this feature for years. Non-destructive filters (adjustment layers), too.

GIMP still doesn't have it. Only in 3.0 it got adjustment layers for filters.