I think the Plaid powertrain is the Pickup powertrain and the standard powertrain going into the S/X and Roadster. I keep going back to Elon's statement about the X being a Faberge Egg, ie expensive to build. Would a SUV version of the Cybertruck take the place the X? It would surely be cheaper to manufacture, higher gross profits, look futuristic and have the CT latest features.
As for the S, they could just replace the battery pack and keep the same body, which is most likely to happen.........................Or a new S will sharing its mechanicals with the Roadster will debut next year with production in 2021. Since we are all guessing.
If there is a "one more thing", it will be a SUV version of the truck.