When you are old like me the 4K for normal functions other than gaming is detrimental. I have issues with 2K.
I second the motion that the PG279Q on a single GTX1080 is a much better fit for card Vs performance. If you try to run 4K on that card you will take a hit in FPS which will make high refresh rate useless. You will also have to lower game detail to keep games playable, low detail at 4K isnt that appealing. I ran the 279Q on dual 1080s in SLI and that was a perfect fit running games at high-ultra detail. Its great for a single card at medium to high detail, depending on the game. Personally I wouldnt attempt 4K with anything less than a 1080Ti and preferably 2 in SLI.
My 16YO just inherited mine so it wasnt going to waste as I went to the PG348Q which I love, but love both monitors.
If you wait on the next technology to come out you will spend the rest of your life waiting. Could be by the time the 4K hits the market your GPU is obsolete.
My advice, go with the best you can afford that is compatible with your machine in the here and now. When I build a new rig I try to do it all at once and not by technology that is on its way out so Im good for 2 years or so. Technology has been rolling out faster than ever. In November of 2016 the Z170 and 6700K was mainstream. December 2016 Z270 and the 770K was mainstream. 6 months later along comes Z370 and the 8700K. Thats 3 jumps in a years time and both the Z170 and Z270 are obsolete with the latter in less than a year from its launch. That was a cruel trick by intel. You cant run a 7700 on a Z370 and cant run an 8700 on a Z270 so that puts you having to upgrade everything.

“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein