We've seen like a hundred (not really but it seems like it) 4K TVs at CES so far, but there are ultra high-def tablets, too. Panasonic just whipped one of these pixel-packed device at its keynote. And it's enormous.
The screen looks beautiful because, duh, double pixels. It looks super thin, runs Windows 8, and it comes with a stylus. But it's TWENTY INCHES. Twenty. You can't carry that comfortably. If it ever comes out, it'll be strictly for professional applications and ludicrously expensive.