You may not have to pony up for a streaming video service (or any service, for that matter) to get 4K video on your TV in the future. GatesAir, LG and Zenith have started field-testing Futurecast, a system that promises to drag over-the-air TV into the modern era. Thanks to HEVC video compression as well as boosts to overall throughput, the technology can stuff both 4K and two mobile broadcasts into a relatively small 6MHz frequency range. With enough bandwidth, you'd only need a set of rabbit ears to watch at least a few basic channels in Ultra HD.
Don't rush to snag a 4K TV just yet. So far, Futurecast mostly exists as a bunch of technologies that will hopefully be rolled into the next-generation ATSC 3.0 standard. It'll take some time before that standard is ready to go, and a while after that before you can buy a supporting set. Still, it's good to know that plain HD will no longer be as good as it gets when you're watching for free.