The industry has been pushing HDR and support for variable refresh rate, and that seems way more useful than 4k@120hz, but it's another thing consumers won't be able to notice unless they try really really hard.
Edit: also, does either DP or HDMI support 4k@120hz? I'm still running my 4k monitor at 30hz because my employer doesn't want to buy me a freaking HDMI 2.0 cable!
The same thing I am going to use the MacBook Pro's 120hz screen for. I think this banal argument can be made for most of consumer tech including why do I need a Retina display when I am perfectly fine with 1080p, but I believe all of these things add up to improve our daily quality of life since we spend most of our time staring at those pixels.
> also, does either DP or HDMI support 4k@120hz?
I think HDMI 2.1 supports it.
FWIW, I haven't seen a 120Hz display without variable refresh rate support. Any resolution.
HDMI 2.1 (January 2017) and Displayport 1.4 (March 2016) support 4K 120Hz.
Of course, 4K 60Hz monitors have been out for years, but are still rather expensive.
There was little to no demand for displays above HD before Apple gave devs the incentives to make their apps support HiDPI by introducing retina displays. Windows took really long time to offer similar support. Linux was (is?) waiting for Wayland to solve this issue.
Look at how much more you can buy in a TV set at a given price than you can buy in something called a "computer monitor"