This was the highlight of yesterday's Toshiba conference yesterday: the 55ZL2.
Toshiba were demonstrating it playing 4K content (presumably from some sort of PC/media server). Even with the usual LED LCD quirks which affect even the best displays of this type (uneven light distribution), I found myself gawping at the screen - the first time I've done this since the first time I saw HDTV footage many years ago.
To give you some idea of what it looks like, here's a quick JPEG of the entire screen with my camera zoomed out (click to enlarge):
And here's what a small detail looks like, zoomed in all the way:
Insane levels of detail.
Toshiba couldn't tell us what the footage was shot on (I'd have assumed a RED camera or something similar that can shoot 4K and higher, but apparently not) but it was clearly a very, very high end video device (not film). Very promising either way.
The only trouble is, of course, other than still images, we have no 4K source so are going to be reliant on the scaler...