Yeah, long way off. SDTV lasted 50 years, you don't think that HDTV will be around for several?
HDTV took MANY years to see widespread adoption and HD was as big of a revolution as going from B&W to color. 4K is a novelty just like 3D. Remember, 3D was supposed to take everything over. 3D was supposed to drive new TV sales. Where is it? No where. No one cares about 3D.
4K will be just like 3D for a LONG time. No one is going to dump a working HDTV for 4K. They will upgrade only when their HDTV breaks and only if 4K is dirt cheap. And only after everyone has one with anyone bother with broadcast content.
Meanwhile for most people with typical HDTV (smaller than 55") at the viewing distances they watch them from, they wouldn't be able to tell the difference between 1080p and 4K unless they were side by side just as they have trouble telling the difference between 1080i and 720p broadcast HD.