If I were spending millions on Epyc servers, I'd certainly test this on a reasonably large sample before committing.
However, that's my thoughts as to why we're not seeing it on Threadripper despite it being on the same stepping. If it were a simple microcode fix (even if you needed to disable some codepath and cut a few percent off) then there is no reason not to pass that down to consumer Ryzen. So far, however, a microcode fix has not been forthcoming. So it's either TR is better binned and thus less subject to the fault, or that something about TR's NUMA layout is breaking one of the necessary conditions for the cache fault to occur.
I do think AMD stepped up their QA after the fault was discovered. I've actually heard of post-week-30 retail samples passing kill-ryzen runs, whereas essentially 100% of the pre-week-25 chips display the fault. However, there are definitely post-week-30 chips that do still display the fault.
I assume what's going on there is AMD is doing a quick run of kill-ryzen to weed out the shittiest chips, the ones that die in seconds/minutes. But since there isn't a way to deterministically reproduce this fault, and AMD can't realistically spend 24h testing every single chip for one fault, some of the only-somewhat-shitty chips are still leaking through their QA testing.
I would take a random week 33 chip over a random week 08 chip for sure, the quality is definitely up, but week 30+ is no guarantee that your chip won't segfault either.