My purely personal opinion on this is that any tradeoff has to be weighed very carefully. For me this proposal can be restated as “Can our most-affluent users get a performance increase if we abandon our poorest users?” If so, is it enough to be “worth it”?
It is easy to try to judge this in terms of our own local values and economies. But in many areas of this world we have some users where the cost of a computer is more than the yearly average income. I personally find greater satisfaction in helping our poorest users use Blender than speeding up the work of those with the most.
That said, “x86-64-v2” (CMPXCHG16B, LAHF-SAHF, POPCNT, SSE3, SSE4.1, SSE4.2, SSSE3) sounds reasonable to me. Seems like a nice change for Blender 4.0 if we announce the change fairly early. This project tends to give little notice about large changes.