So, I've successfully managed to make a HDR video that actually triggers my TV into HDR mode. While I did not use Vegas to do it (it was a timelapse), it is quite possible (I think, at least, more on that below.) to use Vegas as the starting point instead of lightroom/LRTimelapse.

*I'm not sure if Vegas outputs video in Rec2020 color primaries. I've seen options to do it in the encode settings, but when I check the resulting files in mediainfo, it still says Rec709... so this may or may not work for HDR. Can anyone else verify Vegas can indeed output Rec2020? I suppose an XML export into Resolve would solve that issue entirely, but that can be very buggy.

Here's the resulting file. Don't laugh, I WAY oversaturated it and plan on doing another version as soon as I get some time... but this is a hyperlapse I made walking down our entertainment district downtown.

Here was my workflow to successfully turn it into HDR...

1. You must start with at least 10 bit video in a wider color gamut than Rec709. For me, I was shooting stills (timelapse), so I had to set my GH5 to record in AdobeRGB color space instead of sRGB, as it much more closely approximates Rec2020. You can also film in HLG mode using GH5 and get Rec2020 natively, but HLG doesn't grade very well. For video, GH5's V-Log uses Panasonic's V-Gamut color gamut, which will give you what you need to convert to Rec2020, but remember, you must be shooting 10 bit for it to work.

2. Cut the video in Vegas, set your project to 32 bit, color to Rec2020 ST2084 (I imagine the 1000 nit variety works well here, since no TVs currently go above that). If you are shooting timelapse, open Lightroom and LRTimelapse and use that combination of programs to edit the pictures. For video, output to ProRes or any other 10 bit format, making sure to specify Rec2020 color space in the render settings (and hoping this actually does what it says it does). Do not make any adjustments to the brightness levels or color of the video at all, only cut it. For timelapse, I used LRTimelapse to render the ProRes file, and it allows me to specify that it has Rec2020 primaries in its encode menu.

3. Import the ProRes (or other intermediate) into Resolve. Click the edit tab and drag the media onto the timeline. You will need a Mini-monitor 4K card or any other blackmagic preview card that can output 10 bit AND pass HDR metadata over HDMI to your TV. Many can output 10 bit, but not all can do HDR, so be on the lookout for that when shopping. Go into your project settings. Make sure your timeline and preview resolutions are both set to UHD 4K, if you see a 10 bit option make sure it is checked. There should also be an option to enable HDR data passthrough over HDMI. Make sure that is checked. Go into color settings, and set it to "Davinci YRGB Color managed" under color science. Check the next checkbox for separate color space and gamma. Here is how that should be laid out:

Row 1: Rec2020 - Gamma 2.4 (for timelapse exported from LRTimelapse as rec2020, for v-log or any other log format, make sure you select that from the first window)

Row 2: Rec2020 - Gamma 2.4

Row 3: Rec2020 - ST2084 1000nit

Then at the bottom, click "HDR Mastering for 1000 nits" checkbox.

At this point, when you hit the save button, your monitor that you have connected to your mini monitor 4k card should flash and go into HDR mode as soon as you call up something on the timeline to preview. This lets you know you are good to go with the grade. From there, use your scopes (right click on the preview monitor, select show scopes) and the color tab on the bottom to do your color grading. Once you have the video colored to your liking, click the "deliver" tab at the bottom. You are going to want to select MOV and DNxHR 4:4:4 12 bit as your format. The file will be huge, so any other 10 bit or higher format will also work, but I was aiming for bare minimal quality loss during this encode process, so I went with the highest quality I could find. Resolve should automatically pass through all relevant color science info to the file.

4. Download Hybrid encoder. An excellent GUI for ffmpeg/avisynth/etc that is free. Import your Resolve output file into it, and make sure you have "high10" set as the profile under the x264 tab, then look under all other tabs and make sure any references to color science are set to Rec2020 (if you see Rec709, make sure to change it to 2020). If you see Rec709 and it is greyed out, look for checkboxes nearby that correspond to name of that section it is in, and uncheck them. You'll then be able to edit it.

5. Render out your HDR compatible file. Upload it to youtube to test it... if it is HDR, after the file has finished processing (about 30 minutes after uploading) you will see it say "4k HDR, 1080p HDR, 720p HDR" etc. in the quality settings.

Enjoy producing HDR content!

Unfortunately, this method does not allow us to specify the maxfall and maxCLL values in the metadata, which is one of the best benefits of HDR (being able to tell it the specs of the monitor you used to grade the video, so you can be sure that every other monitor sets its settings accordingly for accurate playback). Vegas could take the HDR world over by integrating all of the above steps plus MaxFall and MaxCLL metadata input all into one app...

I'll post a re-graded version of the above timelapse, as well as a few new ones, when I get some free time.