Same pattern as change from EV-DO Rev 0 to Rev A.
When EV-DO was upgraded from Rev 0 to Rev A customers had to suffer with modems that used to much power and handsets with short battery life. It took several years for carriers to upgrade all of their towers. Now the same problem with the change from 3G to 4G. Modems use to much power and Handsets have short battery life. Wait until 5G is announced and by that time ISP's should have most of the bugs worked out of 4G.