Bracket matching will be added to the CodeMirror syntax highlighter on the first wikis. The first wikis are German and Catalan Wikipedia and maybe other Wikimedia wikis. This will happen on 27 January. 
The new version of MediaWiki will be on test wikis and MediaWiki.org from 26 January. It will be on non-Wikipedia wikis and some Wikipedias from 27 January. It will be on all wikis from 28 January (calendar).