> Make it fast on older desktop, by writing asm for SSSE3+ chips
I guess 5 years ago (around the time when Intel stopped making SSE-only chips) is technically "older", but I wouldn't prioritize avx2 when devices intended for consuming media definitely experience much less pressure to upgrade than workstations…
Almost every Intel CPU released since 2013 has AVX2 support. Some Atom SKUs were longer holdouts, but the fraction of x86 CPUs shipped in the last decade that have AVX2 support is very high.