I think we need a different default format than Markdown. Markdown has never had a single standard. Tables were invented by GitHub and were never included in the CommonMark standard. Line breaks are weird for non-Latin languages like Chinese, and for historical reasons, you need two asterisks (**) to bold a word. It is also troublesome to parse.
We need a better markup language.
Relevant xkcd: https://xkcd.com/927/
The nice thing about standards is there so many to choose from. Sure, we can add another one.
AsciiDoc solves a lot of problems Markdown created, but it's got its own problems. At least it doesn't just inject HTML tags all over the place to work around limitations.
I'd settle for just saving CommonMark files with a dedicated file extension, most people think of CommonMark when they say Markdown anyway.