I would guess after Apples lame 10.4, I mean iOS 11 preview, that iPhone fans on the fence going to Android, will absolutely jump ship now to Android, after today major disappointing preview.
No. 99.9% of IOS users are not folks on forums or WDC conference watchers.
They like the phone they have and iOS by extension.
Predictions of mass exodus are simply silly. There is a reason Apple sells 50 million phones or so a year, and it isn't because folks are all waiting to jump ship.