I havent proposed any particular mechanics for my suggestion : its intended to be discussed and maybe from that something can be produced for the devs to consider : Unless involved in port control, there is precious little for a nation to be doing as it stands : I reckon fewer nations will create bigger nations, with a better income outside of port tax income : this may push them to not just consider port control but be in a position to fund such a move, rather than as now, rely on an individual with ambitions and deeper pockets than most.
I see 20 nations (plus pirates) coveting 21 ports as a splendid recipe for action, intrigue and combat : with or without diplomacy adding to the mix. In fact, with diplomacy, the prospects for conspiracy and intrigue as alliances form to take down another nation then disband and reform to defend against another could provide hours of entertainment.