I can totally understand Tesla removing the sequence # to prevent people from complaining about out of order deliveries.
If the backlog has been brought down sufficiently, the sequence number could be replaced by the "delivery window". Though this will only make the inaccuracy of the delivery windows more of an issue; previously people would say "Oh, well, you're 5000 reservation numbers ahead of the most recent delivery, don't worry, everyone is delayed"; now everyone will be staring at the delivery date windows and freaking out even *more* when they don't get their cars on time.
It's gonna make it a LOT harder for MichiganModelS to track the reservation rate, however. We're going to have to wait for earnings calls and press releases now. Or perhaps we might be able to do something with the actual reservation numbers; I suspect they have an issuance sequence which someone can figure out.