I also believe that 4K will be relevant in a couple of years.
Think about it. When more and more people started adopting 1080p monitors, high-end GPUs were still struggling to maintain an average framerate of 30 in games with maxed out settings even at 1280x1024. 1080p was unplayable without multi-GPU setups.
Today we're in better shape. A single 290X/780 can easily put out 30FPS with reasonably good settings at 4K when gaming. Dual 290X/780s can even max out games (minus the AA which isn't needed) at 4K with >30FPS. In a couple of years we'll have single-GPU cards which will be powerful enough to handle a maxed out game at 4K with pretty nice framerates. The graphics hardware to support 4K is already here.
Bandwidth limitations and outdated display interfaces is the only thing holding us back, and a couple of years is plenty of time to take care of that. The only thing that can't be achieved in this timeframe is making 4K streaming possible, but this is of minor importance. Who had the internet bandwidth to stream 1080p content when it became mainstream?
Monitor companies can
make 4K mainstream. It all depends on us the consumers. As long as we're buying 1080p/1440p monitors they have no need to release new tech for us. Also if we start adopting crazily expensive 4K monitors (>1000$) they'll have no need to drop the price (just like it happened with the Titan).
IMO, the key to making 4K mainstream as quick as possible is to stop buying current monitors and to not jump on the 4K tech before it comes to a reasonable price. Doing anything else will delay 4K adoption and make it less affordable.