If you've played WoW, or an MMO like it, just think of it this way. All the experiences are mostly the same no matter how many times you do it. With slight variances based on your class, of course. You go and kill the monsters and finish the quests, and it's all completely predictable. You change nothing. You build nothing. It's all a pre-planned ride. With stuff like dungeons and raids, it's a pre-planned ride you can go on multiple times. With NPCs basically playing the same role as those people in parks wearing character suits.

And it's not just the rides. There's all sorts of prizes, souvenirs, and events designed to make you come back over and over again. There's a casino aspect to it too. Take the ride and you might get a fabulous prize at the end. Or more likely not, but you can always try again tomorrow.

So you can see how the MMO -> Theme Park Tycoon would work. Instead of rides, you designate zones, quests, & dungeons. Instead of hiring costumed people to dance around, you create NPCs. Instead of drink & toy vendors, you sell buff food, pets and mounts and gear. Instead of hiring janitors and security guards, you'd hire game masters (GMs) who would do the same clean-up & refereeing work.

Done properly, this would be an incredible experience. There's the tycoon part of it which would let you see how well you built your Skinner box and how much the Sims are getting addicted. And then there's the part which resembles many of the various gamemaking kits out there. RPGMaker comes to mind. The player can build an entire fantasy world. With multiplayer and the ability to import creations, the world can be built by a team. And then the player could open up the world using the built-in server and actually play in their creation with their friends.

From a layout perspective I can kind of see it working.

  Rides <--> quest areas.
  Class trainers <--> Bathrooms.