One of the kernel maintainers Martin Blumenstingl continues to poke away at the Meson 8 codebase and (coincidentally) in the last week he got CVBS output working. As long as he continues his efforts I'm confident there will eventually be a Eureka! moment
I hope he doesn't lose courage with poking around to get hdmi working especially now we have lima in mainline. I still have the impression the S812 is more powerfull then the S905.