I'm going to guess that they'll have demos at the Apple Stores when it's for sale. Not before that point though.
I don't think that Apple wants someone to walk into a store, play with one, and then ask to buy it, only to hear: "Um, it's not for sale yet.... come back in a few weeks."
Not everyone follows Apple as closely as us idiots.
I agree that they won't be on display until they are for sale, as is the case with each next gen iPhone. This will help the sanity of the Apple store employees. I once saw someone try to buy the display iPhones when none were in stock. But I doubt Apple actually cares if their store employees are pestered relentlessly, it's probably more of a supply chain/manufacturing issue.