At one point, Verizon would not activate an AT&T iPhone 6, even though that phone has CDMA capability, but would activate a SIM-free phone. Verizon has now changed their policy and will activate any iPhone that has CDMA capability.What more benefit would there be in Apple releasing a "sim-free" version? What would be different?
At this point there seems to be little reason to not buy the AT&T version.