Thanks for trying the game ! Glad you liked it :D
I see what you mean about Underwater cities, they also match our look, with domes and tunnels connecting everything ^^
About decoupling the rhythm and building phase, we were supposed to do it originally but had to scrap it due to the time we had left x) But we're happy to know that our first instinct was the good one :)
All other ideas are really nice, if we ever think of pushing the idea further, those would definitely be points to explore ^^