As bad as it may sound, I feel multiplayer wouldn't be so bad as everyone thinks.
Instead of these useless NPC characters that assist you you could have your online friend adventure along with you in a huge world.
Imagine being able to create your own shops in the game where you can set your own prices and all other players will be able to purchase from.
Co-op in dungeons and such would be incredibly fun.
Multiplayer doesn't mean the single player would have to suffer.