I believe the pictures that started this thread were taken near the design center and the two front seats were different colors. That sounds to me like that particular car is a technology and feature test mule the design center retains for their use. It may be an idea that got as far as the prototype phase and those lights may or may not make it into production.
As for whether the X will kill the S, I doubt it. The S might see some drop in sales, but I have little interest in the X. If I had unlimited funds (which I don't), and I needed a good hauler vehicle, I might consider buying an X and removing the two back rows of seats. The cargo capacity would probably approach a panel van at that point. However, I have only been looking at sedans for my more real world plans for a new car and the Model S is almost exactly what I was looking for. I drive a 1992 Buick with the same wheelbase as the Model S today. It gets decent gas mileage for a 92 car (16-18 around town and 25 on the highway), but I wanted something better. From all my research into ICE sedans, some mid-sized sedans had decent gas mileage, but I couldn't fit in them comfortably (I have very long legs), all the larger sedans had barely any improvement over what I drive now! On a whim I looked at the Tesla after crossing a lot of cars off my list and even though it is a major strain on my budget, I don't think I can consider any other ICE cars.
There is a Ford dealership on the way to our house. Since I started looking at cars, I would always look on their lot as we went by and just check out the cars. When I started, I was predisposed towards a Ford, it is the most convenient dealer to home. But pretty much all they sell are SUVs and pickups. They only have a few cars, most of them used. After crossing all the trucks off my list pretty quickly, I was left with the Fusion and the Taurus. The Fusion can't get the seat back far enough and the Taurus, despite being a big car, can barely get the seat back far enough. It's right on the edge. And it's the heaviest large ICE "family" sedan sold in the US. It would have been a lateral move gas mileage-wise and it was kind of gutless.
Anyway after investigating the Model S, I now look at the Ford dealer and think "dinosaurs"! The Model S could use some better storage around the front seats, but other than that, it's almost exactly what I was looking for, even if I didn't realize the electric would be "it" until I looked. Energy cost-wise we have some of the cheapest electricity in the country, $0.08/KWH, so charging at home is very reasonable. A heck of a lot cheaper than buying the carcases of ancient plankton in liquid form. Gasoline prices here are consistently higher than most of the rest of the country. I skipped over even considering electrics because just about all but the Tesla are pretty ugly, almost certainly too small for me, and have paltry ranges. I need a car that can make it to California and back somewhat faster than it took to get there before the railroads were built!
So no matter what the X looks like or has in features, I'm buying a Model S when I get the money together.
I wouldn't be surprised if some innovations are added to the S line when the X is introduced, but I doubt they are going to do a body redesign anytime soon. At the moment they have an iconic shape in the S and they need to keep that until the brand is established with a number of car models. Changing the tech or various trim features will probably continue as they go along. If the new bit fits into the hole the old bit used, or a new hole can be added easily for the new bit, that's pretty cheap to engineer. Redesigning the metal-work is a lot more involved process and I don't expect that until 2020 or later.