They are not looking to replace wikitext in mainstream MediaWiki use (e.g. Wikipedia). However they are looking to figure out how to better interop with markdown, especially with copy-pasting.
There may be some consideration that the commonmark community might want to do to at least see if there is any considerations that can be done to assist in mediawiki’s attempt to support wikitext and markdown interoperability.
E.g. Consideration of how wikilinks can be converted to markdown links and back?