Word has it that the AES XML audio metadata schema will soon be finalized and made available. This has been dragging on for years, but I’ve been given a copy of the almost-final schema (under the usual confidentiality requirements), and it looks stable to me.
AES moves at its own pace, though, so “soon” probably doesn’t mean this week or even this month.
Mad File Format Science 
Any more word on this schema? I have a digitization project waiting with baited breath for it. I couldn’t find mention of it being presented at the AES Conference this weekend though!
Your best bet might be to ask David Ackerman at Harvard’s Loeb Music Library. I don’t like to post people’s email addresses without their permission, but ?his contact information can be found here.