The prolong of this game has no limits, multiplayer is one. Bethseda could one day put out an arena option, say there were arenas in cities where we could challenge other players online. This could be done, think of that viking game Rune with the arena multiplayer option and still ther are players slashing it out with others online today and that game is like 8-10yrs old. I wish I could play Rune online more but the servers running are always somewhere on the other side of the planet Scandinavia or Germany my ping is always in the 300's so I mainly stick to lan matches.
What I would really like to see and is probably impossible without making a whole new game is in Skyrim if we could do the pvp thing in the game world - assassins waiting in the shadows while you are happily of on a quest and he/shes about to ruin your day. Archers being a pain and taking you out from a distance, mages arcaning yur ass and the plate wearer going all conan on you and taking your loot if you lose the fight, yes lose the fight then a percentage of your precious loot goes to the victor & maybe with bounty hunter quests where a player is marked for death - would be assassin heaven. Not an mmo no go collect 30 spider eggsacks ect you quest as normal but the game world is pvp enabled. Skyrims world is perfect for this.
Wishful thinking...