"Excavation mode" you mention... This is an interesting idea. Would this differ from auto-tiling walls, then? How would it know which wall to use? Just endpoints?
"Multiple states"... This is an interesting idea. It might make editing a bit confusing, though. How would you display it when someone is just scrolling around the map editing here and there? I do like the idea. The server would have to reparse the entire sector, since much of its data is stored per-sector, but that wouldn't be wild. "What do doors and traps do at the switch?" is a question, especially if they could be added/removed by the edit.
Terrain height is something I have planned but it will need a new map format first. Who knows how long this will all take.