https://www.mediawiki.org/wiki/Writing_an_extension_for_deployment says "Communicate your ideas/plans to affected wikis to garner both support and suggestions/feedback". In our conversations we have mentioned Meta as a good candidate for a first wiki. An alternative could be mediawiki.org, where technical novelties land first frequently. Opinions?
Note that enabling Newsletter in multiple wikis depends on our plan for T110645: Interwiki support for Newsletter extension
Request in mediawiki.org: https://www.mediawiki.org/wiki/Topic:T2dqjshzbmpgnrbp