I'm thinking along the lines of the Thieves' Maze form D&D: The Movie, the Holodeck from Star Trek: TNG, Deathmatch, Capture the Flag... anything where one or more players can step into and have a little action. It could be used for various purposes: rank advancement, settling grudges, tournaments, practice, or simply killing time.
It'll be easy to build your own dungeons for NWN (as demonstrated in the videos), but nobody builds a new adventure every day. In order to have something to do after all DMs need a break, we'll need some thingy that randomly generates dungeons.
Different "modes" could be made for different classes or Wings. This adds variety and is useful for determining who the best thief/priest/fighter is. A few examples:
A maze with bits of treasure guarded by loads of traps, locks and monsters. Thieves must navigate the maze, pick locks, disarm traps and avoid or backstab monsters. The one that gets out with the most cash is the winner. Multi-Rogues will stand a better chance versus the monsters, but will have more trouble with the traps and locks than pure Rogues.
For the Divine Wing, substiture traps, locks and treasure for undead and "dying party members". The one to save the most lives (either by keeping undead away or healing the wounded) is the winner. Multis can still participate, but face a harder challenge.
For Fighters, Barbarians and Monks, the simple slugfest will do nicely. Fighting in an arena with bits of hostile environment (acidic vapors, for example) will seriously hamper spellcasting (but not make it impossible). That way, the Idiots should easily defeat the Brainers when fighting on their home grounds.
If anyone thinks this would be interesting, I'll try to build a suitable randomizing Testing Grounds once I get NWN in my hands. I'm sure that, with NWN's C-like scripting language, there wouldn't even be a need for a referee. On my own, I could probably make something small and slightly randomizing, with a couple of modes. With help, much bigger projects are possible.
Suggestions? Encouragement? Criticism? Wanna help?