It has been quite a while since the transition from SDTVs to HDTVs, it was a huge and noticeable leap, Full HD was less noticeable but a well-received addition which has become the standard for some time now. 4K has been here for over a year, but the adoption of displays supporting this kind of technology has been slower than expected as people don't seem to notice the difference at the distance they would normally watch their TVs, so the prices on larger displays would have to go much lower before users start to adopt this, as this is the main benefit of the increased resolution. Certainly the lack of 4K content doesn't help to make the transition a little faster.
On mobile devices, Apple was one of the first companies to integrate a high resolution display in the iPhone 4, surpassing the 300 ppi which that company made consumers believe that that pixel density was more than what the human eye needs to distinguish individual pixels. Some time later, phones with larger displays started appearing, but also, the resolution was increased to HD and then Full HD screens were available in sizes of around 5-inches, resulting in over 400 ppi, the difference was noticeable enough to keep those kind of screens even today in some flagships. Of course there are screens with QHD but just like in the case of the TVs, this seems to be an overkill rather than something essential in a flagship, perhaps the main benefit would be VR headsets, as the phones are held much closer to the eyes than normally.
It was recently discovered that YouTube now shows a label for 4320p videos, that's 8K or a resolution of 7680 x 4320 pixels, or for those of you keeping count, 16 times the resolution of Full HD. The example is a video named "Ghost Towns in 8K" and it was recorded with a 6K RED Epic Dragon camera and then scaled to 8K resolution using Adobe After Effects. Clearly, TVs and monitors supporting that much resolution are not ready for consumers, although this resolution has made its way through some theaters but even then, it's not that common. Today's average (or even some in the high-end) computers are not even able to handle the small amount of 4K videos at 60 fps and certainly a high-speed internet connection is required which is also not available everywhere. This is just a taste of how we will store our memories or artistic creations in the future and compatible hardware shall be available soon enough.