[fandangos]

That does not matter. All the mkv bits (which check for the profile) are patched in from externally. FFmpeg does not remove certain features from 4.1 to 4.3.
Other than that: Is there as of now any other devices than the Shield, that is doing DV as half-baked (firmware bug in shield) or even better? Or do we currently discuss a Shield-Only feature here?

Does Plex support "Adjust Refreshrate to match video"? Or is it just running with 60 hz fixed? Means: Is the testing that you guys do comparable?

Plex does have Refreshrate capability but it doesn't seem to work, so it's running at 60 hz fixed. Knowing this now, I decided to switch Kodi into 23.98 refreshrate fixed and remove the advancedsettings.xml. Doing this has allowed the dolby vision mkv movies to play immediately without issue 95% of the time. If I revert back to allowing Kodi to change refreshrate, it fails pretty much 95% of the time.

This is very setup dependent.

Here refresh rate switching actually helps in the odds of perfectly playing the movie.

Having the receiver on, increases even further.

I'm aware that my Denon receiver actually fixes some hdmi timings that some TVs don't like.
I know this because of the OSSC (open source scan converter) that would not work in 5x at some refreshes while direct hooked into the tv and the same resolution and refresh works if you use the receiver in the chain.

And Fire Stick, Windows, does any of those plataforms even expose their APIs for Dolby Vision?

Nvidia does have a bit for Dolby Vision but beyond that has nothing for players to send the metadata to the display.

So I guess Android and very select boxes are the only possible solution for now.