Chad published the MDX specification as an Internet Draft (I-D) today. Have a look at http://tools.ietf.org/html/draft-lajoie-md-query!
Adam Lantos from niif.nu has contributed code to support GIT repositories as metadata stores. The GIT model is perfect for metadata management since it allows very easy separation between metadata management and publishing. GIT supports various distributed models for document management making it easy to integrate GIT in an existing metadata management workflow. GIT also supports signing tags with PGP which will be explored in future versions of saml-md-manager.
Yesterday the project wiki was finally setup. The saml-md-aggregator has been living a solitary life on my laptop hard-disk for almost a year until I decided to get my act together and finish something other people could play with. My hope is that saml-md-aggregator will be a useful tool both for production and experimentation with federation-style trust management.