The new version of MediaWiki will be on test wikis and MediaWiki.org from 16 April. It will be on non-Wikipedia wikis and some Wikipedias from 17 April. It will be on all wikis from 18 April (calendar).
You can join the technical advice meeting on IRC. During the meeting, volunteer developers can ask for advice. The meeting will be on 17 April at 15:00 (UTC). See how to join.
Wikidata will get a new constraint status called suggestion. This will change how the WikibaseQualityConstraints constraint checking API works.