Hard to say, the sales numbers of the S/X have been not horrible, but impossible to say how many lost sales they have had. My best guess is at least 25%, probably more like 50%. But that is a total guess. Mostly based on the fact that whenever I show photos of it to somebody they think the yoke and no stalks is idiotic and not not something they would ever consider. Same boat for me. But Neither me or most of my friends are in the market for something in that segment. We are mostly all in the Model 3 segment though.
It will be interesting to see how well Highland sells long-term if they go through with no-stalks though. My best guess is 2-5 months of very solid sales from the true believers and Tesla/Elon stans, then down to ~50% year-over-year as everybody else rejects it. Another question is if the sales do tank will they be willing to actually understand why, and backtrack to fix it? If Highland is anything like the S/X refresh, the old 3/Y stalk+clockspring assembly will still be mechanically/electrically compatible and it would just require some software (and the old cowling with holes for the stalks). They will still be using that part in the Y, so sourcing should not be too bad. But this kind of responsiveness is not in Tesla/Elon's character.