For a variety of reasons, but mostly the screwy licensing relationship between Bioware, WotC/Hasbro and Infogrames, I doubt this would ever be possible with the NWN (or any other TSR) content and probably not the Aurora engine[1]. With a carefully coded engine and enough bandwidth I could see a server instance that can handle 1,000 concurrent players easily.
Because of some of the past friction between Bioware and the other two, Bioware is developing their own setting and rules and I have my hopes that they'll be less hostile to the idea of PW's asking their players for a fee (especially if they realize that they can get a cut of the action).
While I believe that altruism has its place in the world, running a PW well needs a certain level of resources and dedication. Consider yourselves blessed if you have a solid volunteer staff. Perhaps I'm wrong but I think the total pool of talented volunteers is limited and if not their bodies, then their free time.
Please understand that I do not subscribe to the Gatesian theory that all code must be paid for.
What's your general opinion?
Would this be a viable means of defraying your costs and possibly compensating your staff?[2]
Do you think it would cause a general revolt among the playerbase?
How would/should this affect CoPaP? (paid vs. free, revenue sharing, etc.)
Again, I apologize if this turns into a bloodbath

John
[1] As if anybody would want it anyway, it just isn't tuned for efficiency, high-availability or high-volume. But that's another rant.
[2] Ok, I did the math: US$10/month across 1,000 players (it could happen) would gross roughly US$120k. After taxes and kickbacks to Bioware that would net maybe US$3-50k. Enough to keep the servers running I suppose. Perhaps you'd be able to hire scripters and builders on a contract basis.