@Paladox and myself are working on T179206: Clone both All-Project and All-Users. However Diffusion does not seem to support the refs/meta/config branch, or at least its not very intuitive (because https://phabricator.wikimedia.org/diffusion/WALLPR/history/project.config/;refs/meta/config works). However it would be good IMHO to display the contents of that branch here in Phabricator Diffusion as well, and fetch their history, etc. Thanks.
The refs/meta/config branch history can be viewed, for example, by clicking in the (diffusion) link in, ie: https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/InterwikiMagic,access
However accessing that info from Phabricator directly is not that intuitive.
Upstream, this is https://secure.phabricator.com/T11502.
However, I think configuration may have changed here so that Phabricator no longer imports refs/* other than refs/heads/* and refs/tags/*, as a remedy to user confusion over commit authorship for Gerrit review refs? So maybe this is moot, since it doesn't matter what the Phabricator UI does if it's configured not to fetch these in the first place.