I am periodically surveying repositories, using a list generated by the OpenDOAR API, to see which of these are serving RIOXX 2.0 metadata records. At the time of writing, 11 repositories are declaring support for this metadata format.
You can see these listed here.
I think that these early adopters are all ePrints systems, using the recently developed ePrints plugin for RIOXX.
For each repository, I have harvested 10 RIOXX records to examine them for compliance with the RIOXX metadata profile.