IMHO this option is confusing to users, since this envvar only affects the CPUID as viewed by Wine, not by the program or any of our Unix-side dependencies (e.g., glibc / gstreamer / ...) that may invoke CPUID directly.
It's reasonable to expect that some users find that the envvar works around their issue, share their "fixes," and we'd get a bug reports from a bunch of confused users that the envvar doesn't actually "override the CPUID."
Also, this seem quite easy to bitrot: we would have to ensure that *all* places that might call CPUID directly stays up to date. Otherwise the CPUID view would be inconsistent across callsites—debugging that doesn't sound straightforward.
I wonder, instead, if we can use (or make) a separate LD_PRELOAD library that hooks cpuid instruction via ARCH_SET_CPUID.