Worked out how? There’s no implementation. It’s just conjecture.
It's right there:
> Our bet that S3 would get it in a reasonable time-frame worked out!
How? This is a technical forum. Unless you’re saying any consumer of S3 can now spam links to their product on this thread with impunity. (Hey maybe they’re using cas).
Pretty much all other S3 implementations (including open source ones) support this or equivalent primitives, so this is great for interoperability with existing implementations.