Yes, i think named spawned npc's would do the game alot of good, ie Nelson for the brits, Blackbeard for the pirates, Napoleon for the french? anyway you get the idea, they could just be very rare spawns in the open world and hold some nice unique loot drops.. obviously they would need to be large fleets so the players would need to get together to defeat them.
Think about it please devs! =)
at the end of the day it would give people something else to do apart from port flipping now and then.