Right now the policy only requires a wikitech-l email for requests for mediawiki/* +2 rights. I think we should expand that requirement to all Wikimedia-deployed MediaWiki code, as that access is sensitive enough so that requests should be seen by the wider developer community and not just the people who happen to follow the Gerrit privilege request tag. An email to wikitech-l has been sent for the past couple of such requests and I think it's worked fine.
Topic on Talk:Gerrit/Privilege policy
This seems pretty reasonable. In the case of Wikimedia-deployed extensions that have no real stewards, I'd imagine a similar level of engagement as we get on the tasks (little to none), but there's a better chance of running into the request via email vs the privilege request board. Opening that to broader discussion/same vetting period seems like a good way to approach this. +1 from me.