While Model S has hit a demand plateau at current prices (which are, by the way, higher than prices when I bought mine), I believe Model X has not. It had very serious initial production speed problems.
The need to supply current-model cars to the showrooms is serious, and I think is actually a priority over satisfying reservation holders at this point (now that the typical waiting time is down to a month or less). Now, this is only true because of *relatively weak* demand (as opposed to "two year reservation list" demand), but it looks to me like they still are production-constrained on Model X.
The thing about supplying current-model cars to the showrooms is that the previous showroom cars have to be dumped on the discounted inventory. This has clearly happened. I'm not sure whether any new cars were specifically built for inventory (bonaire might be able to figure this out) but I think the larger factor is that rotating out the entire showroom fleet leaves quite the pile of cars behind.
I know lots of people who will absolutely NOT buy a non-inventory car. They need to have driven it to decide to buy (and that specific car...).