Following similar suit as the iPhone 8 and 8 Plus, Apple will let existing iPhone Upgrade Program members obtain pre-approval for their iPhone X purchase early.
From Apple’s iPhone Upgrade Program site:
Get a head start on your upgrade to iPhone X on 10.23. Use the Apple Store app on your iPhone to get ready for pre-order so you can speed through checkout on 10.27.
According to the page, it also appears those upgrading to iPhone X will be able to take advantage of the new Trade-in Kit process:
If you’re upgrading online or with the Apple Store app, you can have your new iPhone delivered right to your door for free. Once it ships, we’ll send you a Trade-in Kit so you can send your current iPhone back to Apple. You’ll also have the option to pick up your new iPhone in a store — often the same day. When you come to the store, remember to bring your current iPhone with you to trade in.
Seems like Apple sure has learned their lesson from last year. Hiccups aside, I really like the program, having been part of it since its genesis. If you must have the latest iPhone every year, this is the way to go. Not to mention it also comes with the convenience and safety of AppleCare+.