First, they're going to need to put in a hell of a lot more LTE towers. I usually turn off LTE support on my iPhone 5 because coverage is so unreliable that 4G is faster.
Won't this also require many more LTE towers than 2G towers to cover the same area? I'm pretty sure the LTE towers need to be packed more densely to sustain the data rates.
All of this means that the older radios aren't going to go away-- there has to be a fall back for voice. People are willing to accept intermittent data, but they expect voice to work always and everywhere. 911 is probably a whole other layer of requirements on this.
While I agree with your vision, the carriers are very reluctant to admit they're nothing but a PHY. They think they offer services and other features that make their bandwidth more valuable. I'm not convinced they're going to suddenly wake up and say, "really we're just a radio modem."