Office Open XML is indeed an open format. And you asked me to provide a citation for my assertion that shows that governments are trying to migrate away from proprietary formats.

For the U.S. URL, I should have probably been more specific: try http://www.data.gov/developers/harvesting

"As part of Project Open Data most government offices are transitioning to make all of their metadata available via a standard schema contained by a data.json file. These are treated just as any other harvest source."

Actually, I should have pointed you to Project Open Data really, found here:

https://project-open-data.cio.gov/

Citations provided!