Licensing problems abound in the spec.

However, just focusing on the technical parts one can see that it's not at all open, especially in the area MS members like to make the most noise about: "compatibility" with old MS formats. The old binary files seem to simply be encapsulated in the XML, which does absolutely nothing for interoperability and still does not fulfill court orders for providing documentation for the old binary formats.

So you still have the same old problem, an undocumented binary file, with an XML wrapper. In this case the wrapper simply adds further licensing problems to what was once a technical problem.