I agree that full atomic would be best but I don't think there's any reason you couldn't do that in Voting Mana. I'm not sure what specifically they've implemented, but it seems like even if they've just gone halfway on that it sets up a framework to go to the full atomic solution fairly easily. Whereas getting there from the current system basically involves rebuilding everything.
It also provides a framework to eventually allow users a choice of how much VM to move within a delegation, which I don't think a basic implementation of full atomic would do.