[direx]

Am I missing something?

All that is needed for real-world HDR video playback support is the following - unless I'm mistaken?

1. HEVC 10bit decoding and a clean 10bit path through the video subsystem and out to the HDMI port.
2. The ability to set the correct info frame elements in the HDMI signal, to flag HDR10 (and carry the right levels metadata) or HLG EOTFs, and to properly flag colour space and white point? (Possibly also colour primaries?)

Correct. BTW, this has been my point for the entire time in this thread

AIUI 1. has been the case with Apollo Lake and similar via Display Port (at least under Windows) - but the lack of an integrated HDMI 2.0 solution has meant that it hasn't been possible to do 2. and insert the right metadata because the DP1.2->HDMI 2.0 external chipset doesn't support it, or Intel haven't supported it.

Pretty much. As far as I understand the HDR infoframe handling needs a tiny bit of support in the GPU, it's not just the LSPCon. The thing is that this tiny bit is missing in the Skylake-era GPUs (such as Apollo Lake). It is present in the Kaby Lake GPUs and the big question now is if Gemini Lake has a Gen 9 GPU (Skylake) or a Gen 9.5 GPU (Kaby Lake) or maybe even a Gen 9 GPU with support for HDR infoframe handling (maybe due to Gen10 display connections or firmware differences).

Since some sites claim that 10-bit VP9 decoding will be possible with Gemini Lake it even looks like we could be dealing with a Gen 9.5 GPU. This would be great, but the block diagram that @DenisDA posted says a different thing. On the other hand I have posted multiple facts earlier which look like HDR could be supported.

Am I missing something ? Aren't they the two basic things required - technically - for HDR support - there's nothing else, other than driver access to the HDMI system to generate the right info frames etc.?

Correct, HDR support is actually just a tiny piece. The much bigger thing is the 10 bit decoding, which will work for sure on Gemini Lake (at least for HEVC).

(Technically you could probably get an Apollo Lake to do HDR replay IF you used something like an HD Fury Vertex to inject the right HDR EOTF and colour space metadata, and had a 10 bit path through Windows?

 I have never seen a HD Fury Vertex but my guess is that it could enable HDR support even on Apollo Lake. You just have to inject the metadata into the HDMI stream somehow and that's what that device seems to do.