Search and Destroy
Basically battle mode where players only get 1 life per round, but where if their was an objective, say a certain ship the enemy team had to sink in order to win the round. It would actually make battle much more interesting and competitive because you can't just go around butchering the enemy to win the round, you actually have to destroy/defend an objective in order to win the round.
I always found these types of servers to be very entertaining because the difference it brought to NW. Examples from the NA side included [FH] Zombies (which was very popular back in the day, but is sadly dead or really never populated) and currently a server called Zombie Apocalypse. Zombie Apocalypse was very interesting the way that scripted because they made sure each unit such as the BlackWatch or the Sailor had their own unique weapons. Unlike FH where you had Player Zombies, they just used ordinary bots with some simple scripting that made them run faster. Just some ideas from my time on NW.
Obviously the Zombie stuff could just scripted into Holdfast which might make this idea obsolete.