if you look at the borderlands series there is a great feature for co-op gameplay!! i like it to join friends in game and help them whit quests, bosses and pvp!
you can also add a region system so friends can conquer a set of regions in a pvp game and a battle to be the region king on a pvp map, or battle together against a HIGH KING army to conqer a gigantic castle full whit traps and puzzels! Also great for the TES construction kit, creating battle maps
annyway when it comes out whitout such a feature i buy it annyway , i realy like the elderscroll series!!!!