so 10 bit monitors have been enabled in el-capitan but you need a newish graphics card and a new iMac.
intrigued by this i downloaded a 10bit ramp test tiff which shows you if you can display 10 bit images.
i have an ‘old’ eizo CG241w and a macbook pro retina from 2013 with the 2 graphics cards (nvidia gt650m)
this is a screen grab of the test image in up to date CS photoshop and a demo of affinity photo.
so it would appear 10bit is enabled in CS photoshop and some ‘old’ computers monitors?