DLC Megaprojects
I've thought about adding megaprojects to the game, like a stadium for the settlement that gives a huge unity boost. Has to be built in stages: 1st stage lays foundation, 2nd stage builds support, 3rd stage main building, 4th stage decorations. Costs a huge amount of resources to build. Late game stuff.
Stadium
Huge Docks
Just a couple I could think of, I thought this could be an idea for DLC for the game.