Hi, after a long long journey... https://www.mediawiki.org/wiki/Special:Newsletters !
The Newsletter extension is a tool to facilitate subscription and delivery of newsletters hosted on MediaWiki-based sites. You can learn more about this extension at https://www.mediawiki.org/wiki/Help:Extension:Newsletter
Any newsletters within the scope of MediaWiki.org can be created. In previous discussions it was agreed to only allow administrators to create newsletters. Once a newsletter is created, their publishers can announce new issues at will without requiring administrators anymore.
If you want to create a newsletter and you need an administrator to do it, we will be happy to help you at https://www.mediawiki.org/wiki/Topic:Txn15jri131au12s
If you want to report problems, request features, or get involved in the project, please check https://phabricator.wikimedia.org/project/board/888/
PS: BIG THANK YOU to everybody involved in this project. Proper attribution and celebration will come in a blog post summarizing these ~2,5 years of planning, development, testing, and deployment to a first Wikimedia wiki.