The forum has a section devoted to Dungeon Craft, the game engine based on the original Unlimited Adventures.
I did for a while. I made some maps and such for it too:http://www.reonis.com/fw/
I also played for a while.In fact, several years ago, I was working with them on some quests to add to their server. But, somewhere along the way they stopped answering emails, and the whole thing fizzled.
I played for a bit back when it was operating, as well. It was fun when you played with others, but just running around solo got a bit boring for me.
[I think the key for a niche MMO like this would be to have regularly timed play sessions where you encourage players to log in at the same time.