Wow... NWN was my best experience in online RPG ever...

Simply 4 Player by Tiaexz, is an attempt to this way.

I've not started to mod this game yet but It may require the direct intervention from the developers more than simple mods, because it seems needs to be changed the way that the engine works. NWN supports dozens of players at same time, persistent worlds are not story-driven like this game, there is a Dungeon Master, and the PvP requires being in different parties. And also, there is the fact that you already have NWN to play like this, there are a lot of persistent worlds working today if you want and its graphics are not so outdated till today.