If I had to wager a guess, probably something like labwc would end up in that role for a distro of DSL's scope and philosophy. However, I think we're still a while away from that, and for the targeted machines, X is still completely fine and will remain so for a long while.
I wonder what they will move to once they have to start using Wayland. Is there a lightweight, user-friend, and stable compositor ? (My experience is that you can choose two, but not three).