Let's develop an open-source media archive standard

By analogy, consider what would be needed to archive paper documents. If you were trying to design a spec that could replicate dollar bills, I think that you would probably need to store a lot of pixels, and complex data about paper and ink composition. But if you were storing text (such as this discussion?), you would need the ASCII data stream, plus [optionally] a tiny amount of formatting/font data. Using the storage format that contains all of the pixels and complex data about paper and ink composition would be inappropriate. An extensible format, that could expand to include paper and ink data, and image pixels is great, but the extensible format should also be able to shrink down and slough off unneeded, irrelevant stuff when appropriate.