In reading through the replies I think I have a better idea on what might be happening. Since TESLA is about to start delivering, and isn't planning on doing the RWD right away, it makes more sense to not offer it until they're ready to start to deliver (catch up on AWD deliveries). Once they are caught up on the AWD, I can see them re add the RWD and start to produce those. TESLA is too smart to turn away potential clients.
RWD owners will probably be called to see if they'll upgrade, but I don't think TESLA will cancel those orders and jump bump them down the line.