The Dungeon Editor needs to be as usable and accessible as possible, if you want to make sure that most people can create dungeons. It shouldn't be a requirement to have to write Lua to be able to create a basic dungeon. So from that point of view, the dungeon editor needs to have a full visual GUI, which is capable of creating everything that we see in the basic game. Yes, this is a big deal and a lot of work -- but will pay off in the long run.
I'm a long-term member of the Dungeon Master forums. We've been supporting this ancient game for the last 13 years. (We're super-mega-oldschool!

) Back in 2000, a clever chap George Gilbert started work on a clone of Dungeon Master called "Return to Chaos". It had an open dungeon format that anyone could edit through a text file. But no custom dungeons were created until George released a full GUI editor several years later. Why? Because it was too hard and too time consuming to work directly in a text file, and average users simply couldn't get to grips with that way of working.
But after the full visual editor came out, the dungeon building community exploded.

Now we have many custom fan-made dungeons for RTC (
In fact, go and play them, some of them are better than anything official! http://dungeon-master.com/forum/viewtop ... 31&t=23916)
Note that there is also a fantastic DM clone called DSB (Dungeon Strikes Back) which is powered by Lua. You can script it to do what you want, but it comes with a good visual dungeon editor called ESB. This is probably a good model for the LoG dungeon editor.
http://www.ojnk.net/dm/dsb/
http://dungeon-master.com/forum/viewforum.php?f=53
By the way, one of our DM community members also created a Random Dungeon Generator for DSB:
http://dungeon-master.com/forum/viewtop ... 31&t=29263
I've seen first hand that simple to use visual editors are the only way you can get mass engagement from your fanbase to create new dungeons. Make it simple and intuitive, and the dungeon-building community will explode. But if it's too hard, requires coding, and has an arcane interface, then it's going to be too limiting for an average non-techy person.