TGTIWLTP: Multiplayer instances for a single player game.

I was trying to explain to Deo the differences between a multiplayer and single player game.
In a single player game you can pause the action and leave things turn based, which I am happy with. no hassle to fetch a coffee or go to the loo.
In a multiplayer game you need to deal with people being AFK and logging in/out.

Deo though that other players (human onse) would give quests to you despite the game being single player. That's cool I thought. Eventually we came up with the concept of multilayer instances. That is in your single player game you enter a Pub, the Pub is hosted on a server and lots of other player avatars are there. Thus you can interact wit them brag/give&receive quests/challenge people to a duel/ that sort of thing. Much the same was that Warhammer online deals with scenarios.
This would also require a mail system to handle trade and reward deliveries. While cool this would require as much work as the normal distribution skill checks I think.