Today Japan Display introduced the world's first 12.1-inch 4K display. Even stretched over 12 inches the 3840x2160 pixel resolution results in the great 365ppi pixel density.
The new display unit measures 273.7 x 164.6 x 1.96mm and offers viewing angles wider than 160-degree. It uses LTPS (low temperature poly silicon) technology, which enables the high ppi and keeps power consumption under control.
The rest of the 12.1" 4K display specs include 1000:1 contrast, 500cd/m2 brightness and 3600mW power consumption with the backlight turned set at its maximum level. If no backlight is used, the display consumes just 360mW.
There is no info when these displays will enter mass production, but it seems unlikely we'll see them in actual products before the second half of next year. Japan Display is one of Apple's suppliers of screens, so who knows, this might as well turn out to be the next iPad's key feature.