If I'm using something (i.e. Content Translation) on a given wiki (i.e. MediaWiki.org), then its sysops should be able to put a big banner (similar to the 'you have new talk page message') which says a message which the wiki sysops deem useful. This would be useful to notify users of things which this beta feature recently broke, improved, or of certain wiki-specific things like how to best use the beta feature in question. Could try for example BetaFeature: namespace. [[BetaFeature:Content Translation]] would contain a message to show to users who have Content Translation enabled. Or "MediaWiki:BetaFeature/$featureNameHere".

There should also be a possibility to include some text in such banners globally for all wikis (such as a quick link to release notes if a new version was released).

After a user closes such banner it should still be available somewhere for example in the notifications from Echo or in the beta tab itself.