Something to keep in mind is that this is effectively a Windows monitor, not a Mac one. The reason for this is PPI: Most Apple displays are in the 100-110 PPI range, with Retina Display Macs doubling that to 220 PPI. At 28", a 3840 x 2160 panel has a PPI of 157, which sits right between Retina and non-Retina densities. This means that on a Mac, you’ll have to use it one of two ways: Either at 1x, where the higher PPI…
It's unfortunate to characterize a monitor that Mac OS doesn't support very well right now as Windows-only. At any rate, UHD looks like it's well on its way to becoming a very widespread standard, so it's not unreasonable to expect that Apple will improve support for it soon.
Specially since changing dpi is usually trivial on any X server since the mid 80's.