If I were in charge, this is the mapgen I would try:
- One medium-to-large sized Spawn Continent roughly in the middle of map.
- Several smaller continents in the world ocean.
- Dozens of islands with some sort of coast terrain at the shoreline to prevent unfairly walling them in completely with no space for proper siege.
- Whirlpool locations are made non-static (they appear and disappear like, for example, Dungeons) and entering one is guaranteed to send you to another continent.
- Moving to smaller continent is meant for voluntary isolation and has intentional downsides: if current Fast Travel system is kept, restriction to not travel across Ocean is kept. Alternatively, if Boston-equivalent is implemented, you need to be on/travel to the Spawn Continent (to teleport there if it will be instance area, or it is simply located in Spawn Continent.)
Additional thoughts: Whirlpools could take inspiration from EVE Online wormholes, which aside on expiring once their timer runs out, can also collapse after enough mass passes through.
In Haven this would/could have following effects and I have no idea if they would make faction PvP better or worse:
Limit how many people can use a Whirlpool before it disappears.
Intentionally delete a Whirlpool by sending people (well, presumably alts) through it.
Maybe the least disruptive version of Whirlpool would be that it exists for a set period of time, during which anyone entering it will be teleported to random lake in continent static to that Whirlpool.
Also, in case there is confusion, "Whirlpool" is called "Swirling Vortex" in-game.