Its already happening as people are getting wise to Apple's strategy over the years. The number is dwindling every year.
"iOS 11, the latest version of Apple’s operating system for its iPhones and iPads, is now installed on 52 percent of iOS devices.iOS 11 is lagging somewhat behind earlier iOS versions. Last year, iOS 10 was said to have
reached 60 percent of devices (as announced by Tim Cook at Apple’s “Hello Again” Mac event on October 27th, 2016), while iOS 9 had been adopted by 67 percent of devices by November 16th, 2015"