What are the chances Zen3 aka Zen+++ is just that, supremely refined revision of the first Zen. Still using pokey and latency starved CCX arrangements, stuck in 4GHz land.... those promised IPC boost better not be just YouTuber clickbait (Didn't both Bitwit and LinusTT buy new personal homes just recently?).
Zen2 had 256-bit AVX added, which is something I definitely would have liked on my Threadripper 1950x (especially because wider-SIMD is amenable to the workloads that you need 16-core / 32-threads for).
Latency is much worse on Threadripper 1950x (Zen1) by every benchmark I've seen, L2, and L3 latencies were improved by Zen+ and Zen2. Absolute latency to DDR4 was also improved.
Its not enough to make me upgrade off of my 1950x, but I was quite surprised at how quickly everything improved. Especially with a 16-core in AM4 / standard motherboards. (Threadripper on Zen2 / Zen3 might be out of my budget now, but high-end AM4 is looking pretty solid now).
Zen2 also improved the CCX communications with their centralized routing chip, such that NUMA is no longer required. (NUMA still improves Zen2 speeds, but its not like Threadripper 1950x where NUMA is basically required if you care about latency at all)
Technically it is just that, much like ICL or TGL is a super refined Conroe.
The 128-bit to 256-bit AVX jump between Zen+ to Zen2 was as big as the Sandy-Bridge -> Haswell jump for Intel. It was quite significant for the workloads that utilize AVX.