So the phones that need it the most...the 5 series and older, aren’t eligible. Real nice, Apple.
None of those iPhones 5s models and earlier will load the modern processor intensive apps nor will they use the iOS 10.2.1 or iOS 11.2 that has the Battery Management System that promulgated this tempest-in-teapot that began this kerfuffle because people had not replaced their batteries.
In addition, the percentage of people who are using pre-2014 iPhones was only 7% as of March 2017, it is much smaller now. The iPhone 5s was released in 2013.