Looks good Krice. If you wanted rooms you could drop a 'roomie' now and again, or when the digger reaches the end of its lifespan you could drop one. Roomies should not check if the space is filled, just let them dig. Overlapped tunnels would be good for doors. Maybe check to be sure rooms don't overlap, and there are at least 2 entrances....
I did something similar with my program at first, but then I created starvation/death when not adjacent to any walls and let them dig without regard to what was adjacent, this created open spaces.
You can see it in my program, the diggers isolate themselves on a block of walls and dig it out, starving themselves.
I can upload a slower version of my program if you were interested in seeing the steps more easily.