I'd say it's too early to say the smart phone is dead. And omg what a terrible site, I had opened the tab and could not even continue to type my post because it made my browser all choppy. Had to close it. Anyway, I could perhaps see the smart phone eventually slow down as far as number of releases and how often people upgrade, but I don't think that time is very soon and I doubt anything is going to replace it any time soon. Maybe the smart watch, but even those are kinda crap now and rely on having a phone anyway. Once they become stand alone, then maybe.
Personally what I'd like to see die is the whole idea that everything is being tied with an external service. Phones, gaming consoles, and now Windows 10 is trying to do the same with your PC. I think even newer cars are doing that now and I can almost guarantee self driving cars will. Stop it, I want my device to be in my full control and not rely on some external service. Sadly most people don't seem to see the value in having full control of your device so I think it will be a while before that changes.