If it's any consolation, Sep will happily use AVX-512 whenever available, without having to opt into that explicitly, including the server parts, as it will mos

If it's any consolation, Sep will happily use AVX-512 whenever available, without having to opt into that explicitly, including the server parts, as it will most likely run under a JIT runtime (although it's NAOT-compatible). So you're not missing out by being forced to target the lowest common denominator.