well, if i think about maxon for example. the bodypaint painting actions can be undone and redone thus there must be a way.

maybe saving the current state into a temporary file? could be too large, i dont know.
maybe only some things get the ability for undo/redo (those which dont eat up to much ressources - i always see cinema and bodypaint use between 500 and 1000 MB RAM;) )

anyway, it looks great and will turn the designprocess much more fun