Virtual Reality has made a comeback in the past couple of years, with the launch of Google's Cardboard, Samsung's Gear VR and on the higher-end the Oculus Rift and HTC Vive. The Gear VR and Cardboard actually run off of your phone, so you don't get the same experience as you would on the Oculus Rift or the HTC Vive. Having said that, it means that the display on our phones matter more than ever before. While QHD displays (that's 2560x1440 resolution) are perfectly fine for watching video and such, it's not all that great for VR. Seeing as the smartphone is only a few inches from your eyes, the resolution doesn't look as good. This is where 4K could really have a place on smartphones.
Samsung seems to think that virtual reality - especially mobile virtual reality - would benefit greatly from a 4K display. And they aren't wrong. Samsung's head of technology, content and launch management, Kyle Brown stated that "eventually 4K screens will become more mainstream" in reference to the Sony Xperia Z5 Premium that was launched at IFA 2015 with a 4K display. He also mentioned that "the screen sizes we've got, there's not enough of a noticeable difference to make it really stand out and be worth that extra cost to the user." So while he does think 4K is the future, it's not the immediate future.
However, Brown does think 4K would help VR quite a bit. Because the pixels would be smaller, and less noticeable when the display is that close to your face, when using products like the Gear VR. Now Brown didn't say that 4K is coming to Samsung devices this year, or next. However he did state that when the company believes its the right time, and at the right point to mass produce a 4K display, they will move to it. The same with USB Type-C. Samsung doesn't want to mass produce a 4K display that won't offer enough of a benefit to their customers. As it would decrease their battery life and performance of their phone, just for the sake of having a 4K display.