Camera is probably the first obstacle. I've got a kid, and I really want to have good documentation of her growing up. If there were a dumbphone with a legit camera, that'd be a big deal for me.
After that, probably maps is the next most important thing that I want an actual smart phone for. I remember getting my first smart phone, and probably the main thing I was excited about was always being able to navigate directly to where I wanted to go.
Almost everything else is tertiary to my needs.