Just to get back on topic I totally see underwater communities appearing after dream of FF is realized.
It is because human imagination is currently limited by energy requirements in most areas.
After we get cheap energy, well get cheap materials and probably cheap labor due to robotization so everything becomes possible.
Other types of communities that I think would become also possible:
Desert cities (think Las Vegas, but smaller many in numbers and self sustaining),
Antarctic cities,
Underground cities,
Floating cities.
Probably later:
Flying cities or at least castles,
Moon/asteroid/other planet cities and communities,
Cloud cities in gas giants
