1st one I think would be if perma-death were included into the game. If you were to kill someone that shouldn't totally be the end. The person should have a chance to be able to still play by entering into an "Afterlife". In this afterlife this person could attempt to ascend to god-hood and attempt to create his own religion thus giving player religions a true divine entity to fall back on. The afterlife option could have hundreds of uses for "mortal" players such as summoning other entities, creating portals from one place to another, tapping their energies into the afterlife, etc. This could also lead to a ton of features for the "god" players who could make an entire realm in they're own world. They could be able to enter into the material realm by being summoned or by themselves, rain down fire (or whatever you would) upon people who betrayed them, give blessings unto they're followers, etc. Of course there should be a limit to they're powers as well as spirits (of which if players don't want to be gods they could just remain in the spirit world and do other tasks of whatever they like to do).