I have a few issues to fix that I've noticed whilst making levels, but next on the to do list is variations on the doors ie: degrees of being surrounded by wall, ally door (would need to be buried under wall or wall-ally-boxes), maybe a door that subtracts progress to let you escape to an easier room, etc.
After I'm satisfied the door variations work I'm going to look at quests for endless mode. You would start endless with an objective. Though it might be hard to have "kill X amount of Y" without knowing if Y ever gets spawned enough for a seed.