bonnie
I play a nice person on twitter.
Remember all the first production goes to employees of Tesla and SpaceX. I can't imagine they've all ordered 2WD.RWD rollout first is because it simplifies production, giving them more time to work out the kinks on AWD. Remember Model S was RWD first as well, before rolling out AWD. It makes sense to me.
What is probably the most likely is that employees that order 2WD will see those before employees ordering 4WD. When Model 3s start shipping to the rest of us, all offerings will be on the Design Center page. So really, 4WD will likely be offered right from the start for the public. (Just my opinion.)