I've read someone quoting Karl Lang saying that the Nec 2180WG actually has true 10bit DVI support (a 10-10-10 bit path). But as you say, there is no operating system or graphics card that supports this today.
Just curious how Nec themselves tested this feature
Maybe they just tried it with a modded old Matrox card or some of the special greyscale cards for the 10bit greyscale displays that Eizo has..
Yes that monitor is 10 bit and it costs about $3500. And there are a number of 10 bit graphics cards. I have one (ATI X1300) and didn't even know it was 10 bit when I bought it. So they might be more common than you think.
See this quote:
"Witness a billion more colors in all of your graphics applications than you would with competing graphics boards
ATI’s Radeon™ X1000 series employs a 10-bit-per-color display engine that renders in excess of a billion more colors than competing graphics cards."
Then in fine print it says you need a ten bit monitor. It makes no mention of operating sytems and applications software.
The X1950 also says, "Maps any input format to 10 bit per channel output."
It could be that somehow the card and 10 bit monitor will display more than a billion colors to reduce banding by filling in between the 8 bit colors. This card is sold mostly for gaming and video so maybe there is a way for it to work for some things. I don't know what happens when you adjust a photo on it with a 10 bit monitor. In any case, I don't know if there are 10 bit printers so what can you do but look at the image? (I'm really out of my field of knowledge so excuse me for speculating.)
Here a link to the card's specs: