Indeed NWN and its Aurora engine are one fabulous piece of code. No wonder it took four years into planning and coding, and one more year for the Linux version.
I'm not familiar with such a project like what you describe, trying to implement the same idea of persistent worlds (and modules) NWN originally did in the Open Source community. The most prominent (not the only one, mind you) Open Source MMORPG game currently is Plane Shift, but this is purely On-Line (a la WoW or Star Wars Galaxies). Another great thing about NWN is that it allows you to play the single player campaign in cooperative multiplayer, adding a bit more replay value to the campaigns. Not to mention the immense amount of modules that the community produced.
Such a model would be very hard to imitate/implement, but it sure would be a very good addition to the Open Source game library.