It's still too expensive for most people, and will be for a few years. I'm happy with 1080P, in fact I just got a new 42 inch LG 3D TV, it'll most likely be out of date by the time 4K comes into it's own. Remember too, 4K is going to suck down a TON of bandwidth, that will wreck havok with most people's home broadband connections and their caps, forget it on mobile with their puny caps and often overloaded networks.
On the "we're at the very beginning of a mainstream transition from Full HD 1080p (1920x1080) to 4K Ultra HD (3840x2160, or 8.3 million pixels" thing, 99% of broadcast tv maxes at 1080i, first we need to get that to 1080P, then work on the 4K thing.