Dungeons certainly won't be there for phase 3 release. But after that, anything is possible.
I'm open to different ideas. Someone has to write text if that is an integral part of it. The other consideration is whether these are just "goody huts for GPs", or if there is something more to them. (Or for that matter, if we still need "goody huts" after dungeons are added.) We don't want anything too complicated. The focus of the mod should stay on developing the character of your civ (though an "adventuring civ" that sends its Warriors and Wizards off to dungeon crawl is certainly a civ flavor).
I haven't set down any hard plans here. But my basic idea is that they could act somewhat like encampments, as a spawning plot for various dungeon dwelling monsters. An army can kill the guardian on top of the dungeon, but only a GP can "clear" it. (This could be permanent or for some number of turns.) Clearing a dungeon has somewhat unpredictable risk versus reward. There would be some typical range of gold haul (from somewhat disappointing to very nice) and monster spawning. But every once and a while you get some scary boss monster or some nice artifact, like a magic sword, a spell scroll, etc.