>In any case, if everything goes smoothly (and I hope it will), that doesn't disprove me.
Doesn't that make your case an empty statement that basically amounts to "you can never be too careful" (and which is always right, no matter the outcome)?
>But I don't see why pushing APFS now as opposed to in a few years is worth the risk of that 0.1%.
Because it improves lots of things with the 99.9% -- SSD utilization, better Time Machine, etc.
Why should you believe me instead of the people writing APFS? You shouldn't. I'm stating my opinion on the matter. I'm allowed to disagree with them, and you're allowed to disagree with me, but "Apple thinks it's OK" is not going to convince me. If it was, then I wouldn't have formed a contrary opinion in the first place, since it's so obvious.
Further, we don't even know if the experts are confident. It's entirely possible this decision was made above them and forced on them. It's also entirely possible it wasn't, we just don't know.
In any case, if everything goes smoothly (and I hope it will), that doesn't disprove me. It could mean that you're right, or it could mean that I'm right and they got lucky. It could also mean that some people are losing data, but not visibly enough and not in large enough number to make the news.
You say "except, at worse, for some edge cases affecting tiny minorities/uncommon setups" as if that would justify Apple's approach. That's exactly the kind of thing I'm worried about here. I have no doubt it'll work for the common case. 99.9% of users will not suffer any problems. But I don't see why pushing APFS now as opposed to in a few years is worth the risk of that 0.1%.