Finally, a device has appeared that is IMHO workable as a desktop UHD monitor: The Samsung 55" HU8500.
55" might be a bit large for most desks, but the screen is curved so the angular issue of the extended width is mitigated. UHD is effectively four HD panels, so in terms of apparent resolution this is like four 27" HD panels arranged in a 2x2. So it's probably larger than ideal (most people don't use HD at 27" - more common is 22" or 24") but it's close.
And it's the only screen I've seen so far that is UHD, curved, and small enough to put on a desk. But it's MUCH bigger than people currently think is 'normal'.
Here's a contrast with a genuine internet 'office' image (actually advertising Green Card immigration services):