Maybe you have read about projects for supporting UOF. Similar approach to the ODF support.
You can check them at:
What I wasn't aware of, is the study to merge both formats. I can extract some text from the article:
One reason has to do with the formats' allocation of their respective namespaces. The Lab described the UOF schema as being much more structured, replete, and flexible, while certain parts of the ODF schema seem more arbitrary.
This seems a real example of a possible future evolution of the current ODF format, sort of anounce at Brian Jones blog. The conclusion was a conversor http://odf-to-uof.sourceforge.net/overview.html
You can check the announcement at http://www.microsoft.com/presspass/press/2007/may07/05-20UOFODFPR.mspx?rss_fdn=Press%20Releases