You sound a lot like somebody who feels that Internet is serious business.
Aside from that, I too am a fan of this idea. People often don't play the NPCs even if they get the permission because they're afraid they'll screw up. So if the NPC is always played by the same person, this inconsistencies wouldn't exist especially if they're played by the continent writer. Of course, if the writers don't have the time for this, we should recruit some people who would be instructed by the region writers on how to rp the NPCs. I'm not opposed to the regular rewards either. It's not exactly that they would get rewarded for OOC stuff. They would write ICly, even if the character in question was not their own.
I think this could work if there was an OOC request thread for each region, where people who want a mod-played NPC register their thread with the link and the summary of the storyline. The mod/NPC writer would then look over it and post.