Why is there an option to enable it?
Like Taylor Swift says, never ever.
Some (me included) feel that Google will release a CDMA Nexus 4 eventually, but not until spring. Sprint has received the last two Nexus phones, and even got their own custom version of the Nexus S that included WiMax radios. Sprint has also been pretty friendly with Google in the past, being the first US carrier to support both Google Wallet and Google Voice integration.
for sprint, possibly. for verizon, good luck! after the nightmare that was the launch of the gnex last year, i don't think google will ever work with verizon again of their own free will.