Don't expect any miner software improvements. Zen3 has no new features, just better performance.
You're not entirely correct about that. Zen3 has vector AES, for starters. 5600X will be arriving to my postbox tomorrow 
I don't think so, VAES requires AVX512. AVX512 is mentioned for Zen4 but no mention of VAES.
They still need to improve AVX2, that will also likely have to wait for Zen4.
Zen 3 mostly improves single threaded perormance.
IMO AVX512 is a bust. It's over 4 years late and still not available on mainstream CPUs.
And anything AVX512 can do, a GPU can do better.