Wi-Fi Offload Now Mostly is a Matter of How Mobile Usage Plans are Built
With the caveat that “being connected to Wi-Fi” is a different matter from “using Wi-Fi,” the incentive to use Wi-Fi offload obviously is directly related to consumer perception of the value of doing so. An analysis by OpenSignal finds that T-Mobile US customers (presumably the customers most likely to have unlimited-usage plans) shift to Wi-Fi access the least of customers of the top-four U.S. mobile service providers.
In the coming 5G era, and assuming data tariffs remain affordable (no particular consequences for relying on mobile networks instead of offloading to Wi-Fi), customers might not find it useful to offload to Wi-Fi.
Assuming mobile data usage policies do not penalize video consumption, while usage charges remain affordable, the economic incentive to offload will be lessened. Also, given the speed fo 5G networks, offloading to Wi-Fi will not often result in better user experience.