It's very misleading to say iUP customers = most loyal customers, been hearing a lot in this forum, it's insane. So the rest of us who shell out hundreds of dollars upfront every year to upgrade are less loyal? The rest of us who upgrade every year and will be shelling out $200-300 extra this year to upgrade to X instead are less loyal? Are we not Apple Fanatics?
Just because you're in iUP doesn't make you Apple's most loyal customer. Millions of people upgrade every single year, by paying upfront. The only difference is we're not in the program because we can afford to pay upfront instead of in instalments (or maybe some of us upgrade via our carrier every year).
The iUP is not some sort of loyalty program, it's an instalment based yearly upgrade program, it's meant for your convenience so you can easily pay in instalments and upgrade every year, if you cannot afford to pay upfront every year or if you don't want to upgrade every year via your carrier. Saves you a little bit of headache but doesn't magically make you the most loyal Apple customer.
Yes, lots of people will be eligible to upgrade.... to an iPhone 8 and 8+, and in fact that's what most people will be going for, because of the high price of X and other reasons. Others who want to upgrade to X will be waiting to upgrade just like the rest of us who pay full amount upfront every year or have been saving up this year to buy the X.
And if productions numbers are extremely low, we might even see Apple change things a bit. Maybe they will launch an entirely new reservation system for the X specifically based on a first come first serve basis and maybe only if you pay upfront. Apple registered a new subdomain this year, called
https://reserve-prime.apple.com/, maybe that's specifically meant to reserve iPhone X.