This doesn't really make sense, for a couple reasons... There are many flavors of markdown. We'd need a standards body, compatibility suites, etc., and for all the browser vendors to adopt it. Meanwhile, markdown is designed to transform to HTML, which browsers already render. Adding a markdown-to-html plugin/step to your web server or publishing process is not exactly the most burdensome thing, relative to everythin…
It's very similar to the Markdown syntax we all know and love/hate, but fixes many inconsistencies in the spec, and also makes it possible to parse a document in linear time, with no backtracking. It is also much fuller-featured than commonmark, with support for definition lists, footnotes, tables, several new kinds of inline formatting (insert, delete, highlight, superscript, subscript), math, smart punctuation, attributes that can be applied to any element, and generic containers for block-level, inline-level, and raw content.
Some examples, showing how Djot would be rendered into HTML: https://htmlpreview.github.io/?https://github.com/jgm/djot/b...