We've been working on the mod editor for the last couple of weeks now and it's finally starting to turn into something useful.
It will allow you to modify pretty much everything except the very core parts of the game engine. You could pretty much build an entirely different game, as long as it's about placing rooms inside a building.
Here are a couple of screenshots including a couple of the models we will be using in the game.
Please tell us what you think, we're open for suggestions.