As 75D's make up a substantial portion of S/X sales, I can't imagine Tesla would decrease production by such a large amount. The only thing that makes sense is if they are able to sell more in specific markets for Q1 -- China comes to mind, as many may be jumping to purchase before end of Q1 before tariffs may go back up again.
Even then, not sure China demand would be enough -- something has to give. Since we're speculating (well over a year now), I am going to predict that there will be an announcement on February 1, 2019 regarding new battery configurations for S and X. This would be after the cancellation window for those that ordered 75's, after the expiration of the referral program, within enough time to still deliver significant new orders in Q1, and before the ~$900M convertible note is due, giving the stock a chance to appreciate upwards.