I was thinking about this for some time already since I discovered DOTA and Legends of League.
However, the low and constantly shrinking NWN player base (online at least) and the fact it would be a PvP Arena type of server which has no supporters anymore amongs NWN community (all PvP Arenas exticted long time ago) and that it would need at minimum 6 players fully devoted for like 30minutes made me to give up the idea.
Bots, even though technically possible (yet extremely hard to implement for PvP purposes), wouldn't be fun for too long as well.
Seriously, anyone who would want to play this type of game is better to play DOTA map in W3 with friends or DOTA2 or LoL with random peoples.