I don't see why performance-critical code wouldn't have an AVX512 implementation in addition to a scalar or SSE or AVX2 fallback, if AVX512 gives a big enough s

I don't see why performance-critical code wouldn't have an AVX512 implementation in addition to a scalar or SSE or AVX2 fallback, if AVX512 gives a big enough speed-up on a large enough number of relevant devices.