I like your idea of identifying if you are new via iCloud registration. I think this event should trigger an extended first-run setup flow that hits all the major accessibility features under the assumption that most new users would benefit from becoming familiar with these features from the get go and how to access them in the future. I know many senior citizens (including parents) who would have greatly benefit from an accessibility settings heavy onboarding experience, related up many of the issues the author mentioned regarding eye sight and vision related age decline.

Sorry, but I've been a iPhone user for many years, and will turn on iCloud about the 12th of Never. You totally give up all privacy for contacts, photos, appointments, etc. the moment you turn it on, and you can never undo that. Apple is NOT trustworthy enough to have that kind of insight into my life. (And Google is even worse, which is why I'm stuck with Apple as truly the lesser of two very definite evils.)

If you don't use a cloud service, then how do you transfer all of your phone numbers and emails when you get a new iPhone?

This is not necessarily true. My parents had a Mac with an iCloud account and managed to purchase an iPhone from Verizon without ever logging into their iCloud account. It's one of the reasons I moved away from Verizon. They prioritized the sale of the device over making sure that people understood what they were buying and how to use it. Luckily, the iPhone is user-friendly enough that they were able to use it fine but they were never even asked if they wanted to enable iCloud and eagerly said yes when I mentioned what that meant.