I looked at some 4K desktop screens and quickly came to the conclusion that the desktop is not yet optimized for it. Even if you get default font / icon sizes right, too many applications will wind up with tiny unreadable text on sub 32" monitors and you'll constantly need to zoom in.
Or, you'll run your monitor in a scaling mode at 1080p, which means you don't really get to take advantage of the extra screen real estate.
If you spend 90%+ of your time on the PC in a game, maybe 4K is ok if you have the hardware to run it decently.
And the market is not adopting 4k quickly at all. 768p and 1080p are still the fastest growing screen resolutions on desktop according to Steam. So at 1440p, I don't think you'll need to replace the monitor in 2 years. More like 4 or 5. Honestly I think 1440p is the ideal resolution for both a gamer and someone looking for more productive screen real estate on their PC.
This is what I want to do. Extra screen real estate is a secondary concern. I want to keep fonts about how they look at 1920x1080, but with a better dot pitch.
I really want 4K for Diablo 3.