I think of Isra's suggestions, the best probably banning/not allowed into certain towns should you kill someone. It's realistic and does enforce better behaviour, especially if it is an important town. Losing inventory won't work very well, without a storage ability, due to the capitalist nature of the game. If you're carrying a rather large amount of trias when you do die, and end up losing it, you may have to start from ground zero again.
Death aside, in my opinion, a perfect MMORPG would allow for development of technology. That is, creation of carts for hauling ore, encyclopedic collections (in character of course) of the different lands, perhaps cardinal points or some other form of set directions (so characters no longer have to rely on "go left" "which left?!"). Of course, it can only go so far, perhaps the gods will intervene before society gets to creating electricity and steam-powered energy. it is only logical that since the characters can read and write, that they start to record their experiences and places explored for the rest of society.