I donno - Verizon still supports 1XEVDO. AT&T still supports GPRS. I would expect 3G to stick around for a while.
See here: http://www.theregister.co.uk/2015/06/04/2020_switch_of_for_telenor_norway_3g/. In many European markets, 2G is likely to outlast 3G due to the installed population of devices using 2G for telemetry (including the UK's collection of government-sponsored home charging points, each with built-in 2G reporting to Big Brother).
There's also the concern about investment spend: while 3G won't be switched off for some time, investment in network improvement is likely to be concentrated on 4G.