It works for sure, but is the result good enough?
Yes, extremely good actullay.
Mostly crushed blacks, or badly saturated whites...
hmm, that doesn't sound like a huge IQ difference to begin with. Most problems in the HDR implementation will be the maximum nits reachable by the panel (is it 1000nits or less?) and the color space as well as contrast. Whether it can maintain decent black (OLED, Full Array Backlight, QLED .. etc) or not. So your limitations are mostly hardware, not software.
How do curent gen hdr tv's do it?
Again as I said, GSync and consoles work through the HDR10 standards. They don't do it through extra APIs or libraries.
FreeSync proposes to bypass the HDR10 standard achieving a claimed lower latency. But it needs special coding and attention to achieve that, it's not automatic. To quote Tom's hardware on this:
" The question of why not simply use the HDR10 or Dolby Vision transport spaces is already answered, then—they’d require another tone mapping step. David Glen, senior fellow architect at AMD, said that HDR10 and Dolby Vision were designed for 10 or more years of growth. Therefore, even the best HDR displays available today fall well short of what those transport spaces allow. That’s why the display normally has to tone map again, adding the extra input lag FreeSync 2 looks to squeeze out.
Sounds like a lot of work, right? Every FreeSync 2-compatible monitor needs to be characterized, to start.
Then, on the software side, games and video players must be enabled through an API provided by AMD. There’s a lot of coordination that needs to happen between game developers, AMD, and display vendors, so it remains to be seen how enthusiastically AMD’s partners embrace FreeSync 2, particularly because the technology is going to be proprietary for now. "
http://www.tomshardware.com/news/amd-freesync-2-hdr-lfc,33248.html