So far, the invitations reported here all have the criteria Tesla outlined for early priority:
-current Tesla owner;
-reserved in store or at the reveal event (earlier than on-line opportunity);
-located in CA
I don’t know how many reservations that represents, but I suspect it’s a pretty small number. In casually talking with people in line in Seattle, I didn’t encounter another current owner. (If my wife hadn’t asked so nicely for an M3, I would have reserved on line. I don’t wait in line for much voluntarily)
From the Tesla Model 3 FAQs:
“Invitations will be sent based on the date and time you placed your reservation, whether you are an employee, if you own a Tesla, and if we have started production in your country.”
Somewhere else they also said they would start closest to the factory.