What is it with everyone wanting AND MP AND SP.
If you want to do both, you have to balance and the design the game so it would work in MP. Think diablo2 and Dungeon Siege.
The game code is drasticly different (ig. client/server architecture).
You can't simply 'switch on' MP with some patch.
The Divinity gameplay tries to focus on a great single player experience. A lot of things simply don't work in MP.
Why don't we let the developers focus on a SP or on a MP instead of forcing them to do a bland MP and SP game.