Serious shortage is a good problem to have.
From Ming-Chi Kuo, via MacRumors:
We have determined that the demand for XS Max is better than expected (3–4 times that of XS). The gold and space-grey colors are significantly more popular than the silver. 256GB is the most popular, and 512GB is subject to a serious shortage because only Samsung can currently ship NAND Flash well. We are positive that XS Max shipments will grow steadily in 4Q18 thanks to demand from Asia market and the gift season.
My take: This is not original with me, but Apple seems to have set up a good-better-best situation. The lower-cost iPhone XR is for price-sensitive buyers who want to join generation X at the entry level. The Max is for those who can afford the best. The middle model is the sacrificial lamb, there to help sell the other two.
Me, I’m on the upgrade program and simply replaced my year-old X with an XS. Same price, same case, surprisingly seamless transition.