You can't have a 4K Ultra HDTV without some kind of 4K Ultra HD content from Sony, right?
Sony said that the world's first 4K Ultra HD content system will be launched with the release of its XBR-84X900 84-inch 4K Ultra HD TV. The TV itself will come packed with 8 million individual pixels (3,840 x 2,160) and possibly enough sparkle and clarity to make you forget to go back to work or to feed the goldfish.
"The XBR-84X900 has a three chipset solution that incorporates Sony’s proprietary and critically-acclaimed X-Reality PRO picture engine and upscales video content to near 4K quality," said Sony's Ray Hartjen. "That’s right, the programming you currently enjoy, whether from cable/satellite or even your favorite movies on Blu-ray Disc, will be upscaled to an even higher resolution."
He goes on to point out that not only does Sony create 4K projectors, 4K upscaling Blu-ray Disc players and 4K Ultra HDTVs, but also 4K professional cameras for production studios. Even more, Sony has its own studio – Sony Pictures Entertainment – that produces 4K content every day. That said, most of that content will trickle down into its 84-inch 4K Ultra HDTV beast.
"In the next couple of weeks, the XBR-84X900 television will ship to customers who placed pre-orders since the product introduction in September," Hartjen said. "As an extra bonus, included free with the purchase will be the world’s first 4K Ultra HD delivery solution, complete with pre-loaded, native 4K entertainment."
The content will be super-cool mind-blowing brag-to-your-neighbors kind of media, not some goofy 4K junk shot as a short demo. In fact, Sony plans to provide full length feature Hollywood productions made available exclusively to those who purchase the 84-inch 4K Ultra HDTV.
"As the leader in the 4K technology platform, you will continue to see Sony refer to 4K Ultra HD because unlike other consumer electronics companies, Sony is involved in the entire technology ecosystem, including making 4K production cameras, producing 4K content, and even installing over 10,000 4K projectors in cinemas across the country," he said.
Sony's XBR-84X900 4K Ultra HDTV is supposedly available this month for a monster price of $24,999.99 USD. Features include dynamic edge-lit LED backlighting, a three-chip 4K X-Reality Pro picture engine, a 10-unit Live Speaker System, passive Full HD 3D capabilities, network connectivity and more.

After all, they have a history of helping push new technology along :-)
after all we have heard of 8K for a long time now.... still 4K is finally beginning to appear.
(at a ludicrous price of course)
I give it 5 years before it starts making a dent in the market at a more decent and close to earth price.
The funny thing is, the most expensive DVD player we have is also the most sensitive one. Even slight dust on a DVD will cause it to lock up, unlike the three other players.
Of course, this is also the exact equivalent of 4 x 1080p TV's stacked together. We do need true 4k resolution content to made available at the same time since you really don't want the original 1x1080p content 'upscaled' into the remaining 3x1080p 'TV's' no matte how good the upscaling (mapping 1x1080p into 3 additional 1080p, I'm guessing, would be noticeable at reasonably close distances).
Did you ask the same question when 720p/1080p tvs came out?
Because its for exactly the same reason why those came out. Better picture quality.
The average viewing distance for living room HDTVs in America is around 7 to 10 feet, depending on the screen size. So to appear "perfectly" sharp with 20/20 Vision like the iPhone 4 Retina Display, HDTVs only need a proportionally much lower PPI in order to achieve "Retina Display" status and have the HDTV appear "perfectly" sharp and at the visual acuity limit of your eyes.
Existing 40 inch 1920x1080 HDTV is a "Retina Display" when viewed from 5.2 feet or more
Existing 50 inch 1920x1080 HDTV is a "Retina Display" when viewed from 6.5 feet or more
Existing 60 inch 1920x1080 HDTV is a "Retina Display" when viewed from 7.8 feet or more
Since the typical HDTV viewing distances are larger than the minimum distances listed above, the HDTVs appear "perfectly" sharp and at the visual acuity limit of your eyes.
Uh, multimonitor setup?
On serious note, I would prefer one 4k res monitor than four 1k res monitors. Less software issues and looking at the bezels.