Attn Luca and ScottThere are some things best avoided as going against community expectations. I would be happy to see flagged revisions deployed on the English Wikipedia but I'm well aware that there is a significant lobby against that of people who believe that it is important that your edit goes live immediately. And with the community somewhat burned by bad experiences with recent software changes now would be a bad time to suggest such a controversial change.
And that is the fundamental flaw with this whole email thread. The question needing to be answered isn't "what increases new user retention". The real question is "what increases new user retention and is acceptable to the most active/helpful existing users". The second question is much harder than the first.