Bit depth will give you a value per color channel between zero (black) and the upper bound for that bit depth (2^n - white). How the image data is encoded in those values is very much standardized for all display colourspaces (though whether the hardware is capable of displaying the full range of those values correctly is a different story).
HDR is certainly not a fad - the current crop of displays are nowhere close to being able to display the full potential of the technology yet (100% of Rec.2020 gamut @ 10,000 nits)
AndrewUnmuted - are you perhaps confusing 'true' HDR with upscaled / gamut mapped rec. 709 material? e.g. taking an existing rec. 709 master and mapping the color to a larger colourspace?
Netflix, Amazon and several other OTT providers have their original content mastered in true HDR from the get go - no post processing 'tricks'. The main limiting factor is the acquisition source, which is why Netflix have gone down the route of specifying acceptable cameras for use on their original content productions.
Still, I don't think HDR is a net negative even if its just improvements in luminance -- LCD TVs are especially bad at representing shadows and I have grown tired of watching thousand-dollar TVs treat dark images like a cheap laptop. Was hoping HDR would do something about that :/