I was predicting the entire Model 3 line was going to push down sales of the Model S. The Model 3 has the newer design, and some are saying the S is looking tired, but the S is a far more versatile car. It's larger with a hatchback as @roblab pointed out.
I think the S is a fantastic car and if I were buying today with unlimited budget, I would go for it in a heartbeat, but if I was buying today I would go for the 3 because it fits within my budget better and it's more car for the money. The S is a better car, but I can't justify it's a $30K better car. If it was $10K-$15K more, it would be worth it and I think that's what Tesla is going to have to come down to.
If the new motor upgrade for the S and X is the same motors as the 3, then Tesla will have a cost savings and they can pass that on to the customer providing a better range car for less money. I also expect the update is going to incorporate as much of the Model 3's parts into the S/X line as possible, which will be another cost savings they can pass on. The S might be selling for $10K-$15K more than the 3 by year's end.
The S is a fantastic car if one has an unlimited budget. 3P really only has better v2 charging and access to v3 charging over a P100D.
Few however have an "unlimited budget". That is why except for corner cases, the Model 3 is the superior choice in almost all circumstances for the same dollar.
I don't think the S and X selling for more than 75K the issue. Right now, we just don't get enough for that 75K -relative- to the 3. In fact, the S and X is WORSE than the 3 for latest/greatest.