I honestly don't think feature phones are going away any time soon; there's a lot of people out there (myself included) who don't need or want a smartphone and are entirely satisfied with a cheaper flip-phone that places and receives calls and (if we want to get really advanced) stores phone numbers. On a smartphone, that capability is always at least one extra click away (unless they just start putting a number pad on the home screen.) That's going to confuse Granny and irritate the hell out of the rest of us, especially considering we'd be paying extra for the privilege of putting more steps between us and our goal.
Smartphones are no longer a luxury item, so it's not like people who don't have one can't afford one (generally speaking.) Therefore, I can't see any reason that people who don't have one are suddenly going to get one, unless every manufacturer out there can get all the others to agree to suddenly stop producing the phones that are still selling in hopes of forcing people to upgrade to more expensive phones - and all it takes is one manufacturer breaking that agreement to bring the whole thing crashing down and leave them right where they are now, selling iOS and Android phones to the people who want them and feature phones to everybody else.
