We need a page under https://www.mediawiki.org/wiki/Phabricator documenting how https://phabricator.wikimedia.org is updated with new upstream version.
We also need to explain (probably on the same page) how are patches and modules supposed to be proposed, tested, and applied. The Puppet - Labs - Gerrit combo.
Daniel Zahn started explaining how this works at https://lists.wikimedia.org/pipermail/wikitech-l/2014-September/078696.html
This is not a superblocker of the launch. However, it is a question that is already coming, and we know that the right thing to do is to agree and document the process before, rather than after Day 1, because of the bus factor etc.