Not to worryI checked the finalized document for the 2002 standard and just found that the proposal was dropped, meaning its not part of the 2002 standard (sorry!).
I haven't heard anything about this being incorporated and it is not supported in the current IBM mainframe compilers.
My suspicion is that if implemented, this will have rather little use. From what i've seen at very many clients is that usually Depending On value changes from iteration to iteration within one execution of the code. Only rarely is the same value used throughout.
We'll see what happens going forward.
If you find newer info, do post it here - many of us would be interested.