I suspect the new model s/x and the new Roadster will share the same base-platform. So two model 3 rear motors and one model 3 front motor for all variants. The platform will have room for two layers of 18650 battery cells (for roadster). Only one layer for Model s/x. The models s/x car body will probably stay the same, but with new ccs chargeport for EU and new interior matching model 3. Full Supercharger v3 support, of course.
Somebody went over the Roadster prototype with a laser measuring device when it was on display somewhere and the dimensions of the Roadster are very close to the Model 3. It's about 3 inches shorter, but the same with. If the new S was built on the same platform, it would be the size of the 3 and would kill sales.
It may not be coming with the next generation of Model S/X, but I could see Tesla taking the platform for the Model 3, widening it and stretching it for the larger cars. That is the trend in the auto business, make one core platform and modify it for different sized vehicles. For an electric car it's even easier to redesign than with an ICE.
I would not be surprised if the refreshed S used Model 3 motors for the standard car and possible one Model 3 and one large motor for the Performance cars, that would allow Tesla to stop production of one motor design with relevant cost savings. They might introduce the Roadster motor layout for the performance cars, eliminating both of the old motor production.
With the Shanghai plant under construction with plans to import cells to that factory, they will want to use the Panasonic plants in Asia to make cells destined to China and move Model S and X cell production to the US. For cost savings, it would be best to use the 2170s. Jason Hughes thought there was enough room in the current pack space to fit 2170s in the existing pack, but the modules would have to be redesigned for the different sized cells.
Ultimately I think the internal goal of the redesign is to share as many parts between Model S, X, and 3 production for cost savings. The refresh of the Model S was mostly parts sharing between the S and X with a few cosmetic changes thrown in. They may dress up the refresh of the S and X, but there will almost certainly be more parts shared when they're done. Replacing the power and drive system with essentially the Model 3 system would probably be both more efficient and get larger KWH battery packs on the road. Performance cars with some of the tech going into the Roadster would allow Tesla to test out some of the new tech for the Roadster in the real world.
