I think that these might already be enabled, I don't know the minimum uarch that MSVC enables, but I suspect that it is already Haswell. I know that the runtime already requires Nehalem for the CMPXCHG16B ISA extension. Haswell was the next tick IIRC. Windows 11 already has a hard dependency on CMPXCHG16B, LAHF/SAHF, and PrefetchW IIRC. We are well within the range of CPUs where I don't think that we will get any incremental benefits without massively increasing the CPU requirements which I am not sure is valuable. It does not however enable any of the SIMD instructions (e.g. AVX2).
Turns out that the AVX2 path doesn't really gain anything measurable so it turns out that this was a false hope.