Originally Posted by Dhruin 
It's an interesting idea (that has been mooted before) but would it actually work? If the competing AI finished a major story link before you even got there, would that actually be entertaining gameplay?
Obviously, you'd have to balance well. No NPC's should be taking away major main plot lines away from you. That would be a bit overboard. The way I envision it, these semi-autonomous NPC(s) would fall into three categories:
1) competing with you for
a few side quests only
2) making a
couple of the main line quests easier if you play your cards a certain way, per quest
3) making a
couple of the main line quests more complicated if you play your cards a certian way, per quest
IOW (to steal a page from PJ's book), dont' go crazy with it. Do enough to make it fun and interesting, but not too much so that it's frustrating. "Eschalon It".