I don't think 1) is entirely true. The fact that they're pushing the S over the 3 like this would suggest that they wouldn't sell out their full production capacity naturally. Of course, it's far easier to put up a couple of web pages than to redesign the car, and they have a long way to go before they have to think about such radical changes.
1) They're still selling as many model S vehicles as thye can make. Perhaps the market will soften after Model 3 introduction or increase on Tesla's manufacturing capacity.
2) Any heavy add-on increases the weight of the vehicle and decreases the rated distance on a single electric charge. From their point of view it's better to let the aftermarket for interior accessories to develop, as then any add-on is at owner's discretion.
3) People who shop on interior will still go to their local Mercedes, BMW or Lexus dealer. Even other luxury brands (Infiniti, Cadillac, Acura) have had a tough time competing with decades of experience.