You folks that want to wait 3-5 years probably buy green bananas too.
There are no guarantees in life.
I will tell you what is a guarantee when it comes to 4K.
It will require multi-million-dollar re-investments for most broadcasters to achieve 4K in terms of both bandwidth and facilities.
You see, right now, virtually all US-based broadcasters are at 720p/1080i. Even if they were to merely upgrade to 1080p, it would require a relatively significant outlay of money to do so; this is by no means a "flip a bit" software issue to turn on or off.
On top of this, we are still a few years away from all standards (think VHS versus Beta) being worked out. Don't get me wrong, we're closer now than we were a few years ago, but this is still a factor. Also, don't forget that HD got hoisted relatively quickly on the scene because the feds mandated a date-certain change from analog to digital for OTA broadcasts; don't expect the same to happen for 4K.
Therefore, this is why you'll see content much more quickly from specialized broadcasters such as Audience or Sports -- after all, getting a 4K camera is the least of anyone's headaches (even my DJI Phantom 3 Pro drone can broadcast to Youtube in 4K/30fps) -- than you will see from the alphabet soup networks.
4K will come, and with it, so will 8K (which cinematographers are already playing with). It's just not going to be as fast in getting here as HD.