I spoke to the service center, they said the regular leather seats were in such low demand that to simplify production, they were just going to discontinue them. Obviously doing so based on what they already had built and in stock. Black being the most popular color, they probably had a bunch of those built and ready for install. They discontinued the less popular Tan and Grey colors a couple of months ago, likely since they ran out of stock. Looks like the black has finally run out as well. No new seats coming, just simplifying the production with a single leather seat option. Not sure about the textile seats, if they'll eventually start offering those only in Next Gen style seats as well. Would seem to make sense since the standard and Next Gen seats are from two different companies.
As far as delivery times being pushed out till February, they're just back to their "normal" turnaround time. Doesn't mean anything. They wanted to pad their 2015 sales numbers, likely so that could reach their 52,000 yearly projection so as to not panic stockholders. Based on only 18 Model X's being delivered today, they put those on the backburner to get as many cars on the books in 2015 as possible. Now that the time has passed to get any more new orders out this year, they'll have to start focusing on filling all the Model X orders. The factory is only so big and both cars will be on the same production line. So they have to do a batch of one, change the equipment around, then do a batch of the other. They're probably going to take at least a full month producing only Model X's.
My dad ordered his car on December 8th and it was in Transit to the service center SEVEN DAYS LATER!!! He picks it up on Monday. So we now know, it only takes 7 days to build a Model S, at most. Sounds like god and the earth!! LOL.
I did the math based on my VIN and my dad's VIN, they're building about 1,000 cars per week. So they're probably going to wait for X number of Model S orders to be on the books before starting to produce those again. Probably the end of January they'll make the switch and just focus on Model X's until then.
Point being, the longer deliver times is a production issue within the same factory and production line. Has nothing to do with possible new design changes to the Model S. The car is still ONLY 3 years old. They've got their hands full with the Model X and designing the Model 3. The Model S is last on the list right now for any "major" changes. If a new body design of some sort (Model X inspired nose, for example), someone would have seen some camouflaged Model S cars running around by now and would have posted videos or photos somewhere, as they did with the Model X. No such photos or videos exist that I'm aware of.
Next change won't be until after the Model 3 is complete in a couple of years. Next change to the Model S will likely be related to new Auto Pilot hardware.