As far as I know AVX-512 is just a wider version of AVX2, and it also becomes more complicated because there are many different flavours of AVX-512 (some with byte/word support, some without).
For a web browser and javascript where we don't really do much beyond 64-bit, it would likely make no difference aside from bumping power usage. It'll be oversized for our typical processing. Not like we're having large data structures that need very efficient processing; we're not doing AI, we don't do video encoding, etc. And even those tasks are more likely to take advantage of NPU or GPU so AVX-512 on the CPU is more of a niche than anything else that likely won't have any real-world positive impact (It might actually be worse than AVX2 because of the overhead)
