I think Elon's messages are a bit mixed when it comes to the future of build to order. To me it seems that this will always be an option for Tesla customers, but to drive significant Gen3 volume Tesla is leaving open the option for dealerships. One way to drive volume is to produce batches of Gen3 with common configuration options and then sell them through national or dealer level inventory. Kind of like "inventory" cars today, but larger scale. If they push this inventory to the dealer level, then this sale could be at the time of the transfer from Tesla to the dealer (like other manufacturers).
Yeah I agree listening to his comments they haven't really locked in on that for GENIII. You might be right, in he end he most efficient for those volumes may turn out to be a batch hybrid model. Apple does that, much different product of course, but works well. Will definitely be interesting to see it play out