I agree, logistics are a problem. That is what I was trying to get at - 4K/120 content is currently a logistical problem (among others). The only source with any meaningful amount of content is high-end PCs. If you want to play modern games in 4K with a solid 120fps, you aren't going to be able to do it with a small and discrete console-like system. You are going to need something bulky, noisy, and hot (not to mention expensive). Moreover, the high bandwidth needed for a 4K/120 signal can be a challenge; a lot of people already struggle to get 4K/60 to work on PC->TV connections requiring a cable run of > 25 feet. So the PC probably needs to be in the same room as the TV.
At the end of the day, a format is only appealing if there is content available for it.
I would like to remain optimistic that 4K/120 will eventually move out of the domain of the super-enthusiast gamer and be supported in mass market source devices - driven both by technical progress in GPUs and rising popularity of VR - but that seems more like ~5 years off to me. It would be nice if video came to the rescue and popularized the format, but HFR movies do not seem to be gaining traction. The one area where I could see there being mass market appeal for 4K/120 would be in sports. However, that seems unlikely to happen any time soon because sports are mostly live broadcasts, and broadcasters are not going to want to do 4K/120 due to bandwidth constraints.
So yeah, I think we'll only get support for 4K/120 if it costs almost nothing to implement and some nerdy engineer at the TV manufacturer feels like championing it. It would at least give them a nice demo reel to show off during their CES presentation.
I think you're forgetting about the "variable" aspect of Variable Refresh Rate displays.
You're correct that a locked 4K 120 FPS at maxed-out settings in new games is unrealistic on today's hardware.
The whole point of VRR though, is that you no longer have to keep the framerate locked to 120 FPS at 120Hz for things to look good.
Old games might run at a locked 4K120.
Less demanding current-gen games might run at 90-120 FPS.
More demanding current-gen games might run at 55-70 FPS.
Maybe some games are a bit more demanding than your system can really handle, and run at 45-55 FPS.
With 4K120 support, it's now possible to run games at resolutions in-between 1080p and 4K too, while still taking advantage of high refresh rate support.
Perhaps native 4K is too demanding but 1440p, 1600p, 1800p etc. give you more acceptable performance, rather than having to drop the resolution to 1080p for >60Hz support.
A mid-range GPU should easily handle 1440p above 60 FPS in most games.
If we're looking at console hardware rather than PCs, maybe a game running at 30 FPS will actually run closer to 40 FPS now that the framerate can be unlocked, and dips below 30 are not going to be as noticeable.
Even if a game is only running at 30 FPS, you still benefit from the significant reduction in latency that VRR brings.
Current-gen consoles will benefit less from >60Hz support, though it may still be important for low framerate compensation on LCDs. Depends what the VRR ranges are.
As gaming hardware gets more powerful, you will continue to see improvements with a 120Hz VRR display.
I'm not fond of the term, but it actually
does offer future-proofing vs a 60Hz fixed refresh display, because VRR allows you to push the framerate to run as fast as your hardware can handle, instead of having to lock to 30 or 60 FPS.
If a demanding game is running at 45-55 FPS unlocked today, you would have to cap it to 30 FPS on a 60Hz display for smooth gameplay while the VRR display would simply run it at 45-55 FPS.
If you then upgrade to hardware which is 50% faster, a fixed 60Hz display should now be able to lock it to 60 FPS, while the VRR display will run it at 68-83 FPS - so you get a lot more out of the same upgrade by having the VRR display.
Another 50% hardware upgrade brings that to 101-120 FPS on the VRR display. With 4K60 you won't see an improvement - it's still locked to 60 FPS.
As for PC hardware being big, hot, and loud, there are
many different examples of PCs which prove that doesn't have to be the case - but this is starting to stray off-topic.
Broadcast or other sources do plan to move towards HFR content. No-one can really say when that will be, but I have heard that some are targeting the 2020 Olympics.
Maybe movies will stay stuck in the past with 24 FPS, but I certainly hope not.
The point is, again, that by having the support for 120Hz the display is
actually being "future-proofed" because it will be capable of supporting this content when it arrives, which is the direct opposite of other technologies that have been introduced recently like HDR, which shipped out in an unfinished state that I would not really consider to be "feature complete" until dynamic HDR arrives with HDMI 2.1