The day Extension:Newsletter is deployed, everybody will ask themselves why didn't we have this feature before.
While this happens, I keep trying to find a GSoC / Outreach co-mentor, and now a hackathon buddy in Lyon just in case this alternative model works better. Someone willing to write a prototype of this MediaWiki extension.
I have a clear idea of what we need and I can help sketching the UI, writing strings, testing, discussing improvements, promoting the features, perhaps even recruiting more people. If you are interested, please check
Possible Project for a Newsletter MediaWiki extension https://phabricator.wikimedia.org/T76199
Public / private questions and feedback are very welcome!