Alright, I know this is probably a pretty crazy idea but it would be pretty entertaining.
If you pay for the game (upfront, monthly, whatever) you get full access to all the bells & whistles. However, there is always going to be another group that can't/won't pay or just wants to try the game out. They get to become.... *drum roll* enemies!
That's right, they get one choice of race (eg. kobolds), only get to travel in their cave and to the surface surrounding their town entrance. They do have classes but they can only get to 3rd level. They also don't get experience the normal way, instead they accrue it purely based upon battle encounters with the paying customers.
So basically you are getting a group of smart NPCs for the paying customers to slaughter. The non-paying ones will team up since they will, naturally, despise the paying PCs. Players test driving the system will get a feel for the classes and game systems as well as a taste of battle.
I seriously can't stop laughing when I think of this system. I'm imagining a swarm of poor down trodden kobolds rushing some 15th level fighter with great cleave. It would be inherent PvP without all the OOC issues.
Oh, mix in true NPC kobolds too in the same faction as the non-paying players.
