A general clearinghouse for metadata would be a wonderful idea.  I think there would have to be some sort of standard set and adhered to when making metadata.  I know I bake up my own for every product I have just because I don't like to have to wade through the multi hundreds of gigs of content I have in my runtime.  This was one of the many reasons I left poser for dazstudio.  Where issues would arise is in how people categorize their content.  I may not use the same filing system as everyone else; so, my way is good for me but maybe not everyone else.