Most likely that official support is dropped, but compatibility is up to each manufacturer. Bit like how 400 series boards can accept Zen 3 but only if manufacturers stated so with their BIOS update. I've also thought the same; 500 boards accept only Zen 2 and 3, so this surprises me as well.
If anything, I'd stick to the BIOS release version stated on each SKU. Best shot for compatibility and all.