I have written a python script to take files that probably have bitrate overkill and make them smaller by targeting a specific VMAF score to suit my needs. In it I use ffprobe to check for HDR metadata, and when it exists I extract it and ensure the encoding job uses the same metadata in the x265 command so the output file is still an HDR file when the input file is an HDR file. I don't see why SPV couldn't do the same thing. I think we can probably manually accomplish this by editing the x265 parameters, but SPV should be able to automate that.
edit: Well, maybe not. An example file I have would need these parameters:
X265 Parameters:
hdr10=1
hdr10-opt=1
repeat-headers=1
colorprim=bt2020
range=limited
transfer=smpte2084
colormatrix=bt2020nc
master-display=G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(40000000,50)
max-cll=1655,117
But when you try to add those manually to the x265 parameters the dialog box doesn't let you enter the last two lines properly. It interprets the commas as new-line characters and you get a bunch of new lines added that are nonsensical as a result, like this:
master-display=G(13250
34500)B(7500
3000)R(34000
16000)WP(15635
16450)L(40000000
50)
max-cll=1655
117
edit2: Unfortunately the parameters didn't work for me anyway. But hopefully the devs can get this working. Doesn't seem like too hard of a job to extract the necessary metadata and use that going forward from there.