There is a slow moving discussion about this at https://www.mediawiki.org/wiki/Talk:Requests_for_comment/Markdown
The bigger risk is that the rest of the world settles on using CommonMark Markdown once it is properly specified. That will mean in the short term that MediaWiki will need to support Markdown, and eventually it would need to adopt Markdown as the primary text format, and ultimately we would loose our own ability to render old revisions, because the parser would bit rot.
One practical way to add more discipline around this problem is to introduce a "mediawiki-wikitext-announce" list, similar to the mediawiki-api-announce list, and require that *every* breaking change to the wikitext parser is announced there.
wikitext is file format, and there are alternative parsers, which need to be updated any time the Php parser changes.
https://www.mediawiki.org/wiki/Alternative_parsers
It should be managed just like the MediaWiki API, with appropriate notices sent out, so that other tools can be kept up to date, and so there is an accurate record of when breaking changes occurred.
-- John Vandenberg