I've been looking for exactly something like this. Lately i've been playing FTB with only wasteland-y type biomes able to spawn in, very apocalyptic.
I imagined a modern-ish style town the size of your average minecraft biome, small houses, suburb style would surround the edges, getting more dense with factories, stores, and apartments as you got closer to the city center.
However I should point this out!
MACE is a program you can use to generate a minecraft save with semi-random generated cities built into your game. You can choose the theme and the population (if any) of the city. And you can decide how many cities you want and how far apart they will be spaced.
The best part is that it only generates the chunks the cities spawn in on, meaning when you move the created save to your FTB folder and load it up, all the chunks outside the cities will still have all your modded ores and other things.
You can even create your own building templates for it to use, but for someone like me it's really confusing so I haven't attempted to create any yet. @.@
I've used it a bit before but haven't played around with it much yet.