I want military and civillian harbors and aerodomes separated. Navy harbor and trade harbor, and cvillian airport and military air base. Have the navy harbor show up in the renaissance era (and make England's dockyard a unique of it, keep Dido's as a trade one). The civillian aerodome should be cheap to build like an aqueduct and allow civillian and faith units to move around with just the district, no buildings needed. The military one should be like the current aerodome.
Some random ideas
Harbor. Gives gpt/gold percent, and maybe one of the later buildings can do something related to trading amenities. Maybe amenities effect 6 cities instead of 4, becuase you're trading more efficiently?
T1 building: lighthouse like normal
T2 building: warehouse. + money
T3 building: industrial dockyard. Think like a maersk dock full of containers.
Navy dockyard: Basically copy of the encampment for boats.
T1: Pirate's cove/Shipyard. One gives boost to ranged + raider units, the other gives a boost to melee units, like the barracks/stable pair.
T2 and T3 would be like encampment's. Lets you build military engineers, gives hammers etc.
Airport. Like the aerodome, has two tiers of buildings. Civillians and faith units can hop between airport districts, no buildings needed.
T1: Shopping pavillion. Gives some money and amenities
T2: Airport expansion. Gives more tourism to the things that get tourism with flight, and also more money.
Military airbase
T1: Guard post. Gives the aerodome a ranged shot like the encampment has. Allows military units, corps, and armies to hop between airbases with a guard post.
T2: Hangar. More planes can stay here. ICBMs can be stored here as well, but still only launched from silos. (Remember, an enemy unit can go pillage a silo, but they won't be able to do easily this here, since, there'll be a guard post).
Bonus idea: a building that goes in the neighborhood district that stops recruit partisans, but lowers the housing capacity but 1 and -1 amenity.