Even if 50% of deployed TVs were 4k capable, the problem is where the content is being produced.
Youtube is rich with 4k content because flagship smartphones and action cameras like GoPro have been able to shoot in 4k for the last few years. So you have a strong starting base there on top of the semi-pro video producers uploading their content to Youtube.
Netflix and Amazon Prime have 4k content, but it's primarily for the content that is being exclusively developed for their content library. So you can watch Stranger Things (Netflix) or The Grand Tour (Amazon Prime) in 4k, but 99.99% of the non-exclusive content tops out at HD.
For the movie rental business, 4k is being offered for some films, but only as a means of extracting more money from your wallet. 4k Blu-ray discs command a ridiculous premium over standard Blu-ray. On Google Play and Vudu, you can rent or buy 4k movies to stream at a higher cost than the HD versions. Apple is offering 4k for the same price as HD on iTunes, but only if you go out and purchase an AppleTV 4k.
When it comes to live TV, look at what FOX Sports is doing now:
College Football Preview: Fox Sports To Produce 13 Games in 4K
Their big news is that they had a single 4k capable production truck that they were sending around to cover 13 college football games, and that's an effort by FOX Sports Labs -- not really even part of their mainstream offering.
We have a long, long way to go before broadcast 4k is anything more than a gimmick.