Shipping dates only slip if Apple doesn’t have sufficient product inventory built up. Last year they had supposedly had trouble with the new FaceID tech, but that problem was solved 10 months and 40 million units ago.
Selling 4:1 XR to XS series is worse than selling 2:1, they want to sell as many high-priced XS products as possible. 4:1 would be for example 80 million XR/10 million XS/10 million XS Max. I’m sure they’d love to sell 1:1 (e.g. 50 million XR/20 million XS/30 million XS Max) but given the attractive price of the XR vs XS I think that’s probably over-optimistic.
After all, the XR is $250-350 cheaper and that’s a big deal, it’ll certainly drive a lot of sales, probably mostly at the expense of XS. The Max, being the largest and best, should have decent demand from those who are less price sensitive.
I suppose the 5.8” model could eventually be discontinued altogether, if demand for the 6.1/6.5 sizes overwhelms/swamps the 5.8. But Apple probably already knows it will sell fine, and by that I mean according to their expectations—not the expectations of analysts.