Ella: Thanks, this is great!
Seriously awesome work.
In re: modded rabbitholes themselves, as far as I can tell, both the terrains (.SC4 equivalents) and rabbithole buildings themselves are straightup ripoffs from Sim City Societies. Riverview adds new skins for some of them, so it may yet be possible to have custom ones? I know they talked up a huge deal about SCS being moddable through C#/XML, and they were supposed to add building modding tools at some point. Hopefully they'll actually follow through on it, once the relationship between SCS files and TS3 files is figured out (or whatever EAxian voodoo the former is pickled in to turn them into the latter).
Of course knowing EA, once we do finally get rabbitholes they'll use it as an excuse to
not give us non-rabbithole restaurants and shops in the OFB expansion, just more "missions" and boring crap to stare at for hours while our Sims "run their own businesses".