I think ipad processors will now differentiate from iPhone chips base on their software. With ipadOS it’s likely that support for iPad devices will have no bearing on when iOS (iPhone) devices stop being supported. It’s entirely possible that the A10 in the iPhone 7 (iOS) could lose support before the A10 found in ipad’s running iPadOS which for all intents will be a software still in its infancy for the next few years.