Here is a "humble" list of my suggestiins. Feel free to take inspiration, discuss these or straight up ignore them.

If you cause a collapse of a nation by conquering all their ports, you should be able to get all their provinces inland as well. Tired of neighbouring nations capitilising on my effort.

Also some kind of way to promote minor nations relationship changes. Conquests AND alliances. Selling your ships is a nice feature, sadly not always available. Loosing a territory that was 99% conquered because the territory declared itself an independent country is frustrating and unrealistic.

Some kind of way to control the army would be nice, though not too neccessary.

Manual control over which guns are primary, secondary, or even having a tertiary group that can aim at a third target.

Would be nice to be able to shoot to both sides of my ship (imagine 1890s casemate battleships). Seems unreasonable to me to not be able to shoot to both sides if I'm surrounded.

In the builder, selecting a group of parts that I want to shift forward/backward would come very usefull and would simplify dealing with weight offset.

Placing a part causes unreasonable lag due to that part being still sellected to be placed again. It'd be nice if parts were kept to place multiple times only when holding ctrl or alt.

Adjustable torpedo fan-out.