Toady, will other races have these sorts of new site divisions at all? I can easily imagine a true distinction between cities and surrounding hamlets for humans, or maybe a goblin dark tower having a clutch of small, scattered camps around it to better protect against invasion and act as outposts. Connected to that, will sites ever "mature" into another class of site, or decay into a less populous class? For example, a regular fortress might seal off the underground due to a forgotten beast invasion during worldgen and become hill dwarves, and then when you went there it'd just be fifteen or twenty dwarves fishing and farming and living in wooden houses, and you'd talk to the elder of the village and he'd say "a long time ago, in my grandfather's grandfather's years, we were a mighty fortress of hundreds, but then a mythical monster appeared out of nowhere, killed almost everyone, and we had to seal it off. The fortress is still down there if you want to dig through and try to slay the beast." Or you'd get legends of minor sites that hide great wealth or ancient artifacts of immense power.
Of course, the lovable not-quite-right-the-first-time nature of Dwarf Fortress probably means that we'll get, say, peaceful farming communities where a small child owns the most powerful sword in the world, or something...
Finally, are we ever going to be able to play as these different sorts of sites? And, will the depth of sites be more variable to account for the different site depths, especially on embark?