I very much disagree with the article. I've seen several 4K TVs, and the picture is amazing. From a typical viewing distance, you can easily see the added resolution, compared to 1080p.

I would go ever further, and say that 4K is still not yet good enough. It looks great, but still not like reality. My guess is that this would need somewhere between 8K and 16K. Contrast and framerates could also be higher.

Sources: my own experience with 4K TVs at IBC 2007 and a recent trip to Japan.