Yup. Elon has said the only reason the S and X are still in production is sentimental reasons. I think Elon wants to keep the bragging rights of having an electric car with highest performance numbers so the S Performance is getting some attention, but it may languish once the new Roadster is out.
If they keep the S and X, I think the next major revision (body redesign) will be to make them into some modification of the 3/Y platform. That is the best way to keep them in production. Right now the S and X have a lot of the same look as the 3/Y and they share some systems like Autopilot, but there are very few shared parts across platforms, which makes the S/X much more expensive to make.
Tesla is tinkering with simplifying the 3/Y platform right now, mostly focusing on Y changes, but the 3 will be updated to get most of the Y changes once they are finalized and in production. After that they may start looking at an all new S that is built on a modified 3/Y platform. The X is going to be more difficult to update if they want to keep the falcon wing doors. If they lose the doors and go with something more standard, then the all new X could be a stretched and possibly widened Y.
They can give the S and X better trim than the 3/Y to distinguish them further, but the 4 cars would share a lot of parts making the S/X far cheaper to make.
I know people talk about Tesla needing a halo car, but I disagree. Car companies make halo cars to distinguish themselves from the rest of the pack. Hyundai is a McCar without Genesis. And even with Genesis it's still a pretty generic car company. The Big 3 American car companies have made some kind of sports cars to draw attention to their engineering and design and get people in the door.
But Tesla doesn't need a halo car to get attention. The public today pays more attention to the 3/Y and upcoming vehicles like the Cybertruck than they pay to the Model S/X. The news of the Plaid S got some attention this year, but the standard S/X is old news to the car industry and the public.
The S/X has a tiny following among people who really want super high performance. An even smaller number of people drag race their Performance cars. But the bulk of S/X sales are standard cars. The number sold have been down since the Model 3 came out because the Model 3 is a better size for a lot of people, it's cheaper, and it's at least 80% of a Model S. The Model Y is a similar Model X killer.
I like the Model S better than the Model 3 and I'm glad I have it. But if the Model 3 were available when I bought my S, I would have bought a 3 instead, even though it's not as nice. If I had to replace my Model S today, I would get a Y. I hate the center screen layout, but it's more car for the money.
