Here are a few suggestions that I would think that could fit in the game.
Seamless map transition
Don't know if someone has already suggested this, but It would be nice to be able to seamlessly change from map to map and not have to exit to the map view to switch settlements. Feels kinda clunky and takes too much time.
Settlement times would be in sync. Just doesn't make sense that the first settlement is in autumn and the second in spring that is just right next to the first one.
Whole map sync
Last thing, that the time would still go on in the other maps and people would still do their jobs and send supplies with couriers as time goes on instead of freezing. It might create some hectic stuff if multiple settlements would need help in the night, but that's the price you pay for not defending everything well enough.
Let me know what you think about my suggestions!