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.