What I'd like to see would be a mod that as a higher level char lets you take over one of the ruined forts and rebuild it slowly, pretty much like the Crossroads Keep in Neverwinter Nights 2. You'd have to man and defend the fort, and you'd raise tariffs and offer protection to travellers and travelling merchants. After a while farms would spring up around the hold, and you could tax them in return for your protection and so on. Add a few quest like a "bandit king" arising or something like that, have other adventurers come to you for work and so on. Maybe even chose a side in the civil war incl. a siege or something. It'd be pure hell to code, a game within a game but I'd love it because I absolutely LOVED Crossroads Keep.