I wouldn't mind the MP as an option for one of the higher stretch goals (or sequel, but that's a long way then...) if it would be done similarly to the NWN - i.e.:
You can go co-op in campagin AND you can create own worlds for hosting Persistent Worlds. - I realize that this would probably require a huge amount of work (release of proper modding tools, etc.) but at the same I would expect this to be a top tier goal (prob. somewhere around 4-5mln mark), so to be done only if all other parts can work well in SP experience.
Co-op would be certainly fun, but for me it would create more carving for a spiritual successor of NWN Multiplayer client
