Excellent. Once Secure Boot is turned off, Haiku Beta 2 boots right up on the Atari VCS 800. It doesn’t see the Wi-Fi, but it looks like the Ethernet is detected all right (I don’t have a cable there to find out right now). It would also seem that the sound hardware is detected, but the only way to get audio out of the VCS is through HDMI.
It also looks like it’s in 4K (the TV is 4K), so that’s something.