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.