Despite text being fully portable, it is limited when it's needed to link a image or other files. People often forget how useful this concept is.
Html is not a viable option as it is awfully verbose for taking simple a note.
Markdown adds just enough semantics that is perfectly readable. From a hex editor to Microsoft Word.
We're in a somewhat critical moment, where markdown can either stay as it is, then dominate and become a godsend format of solid usability for decades, or a harmful feature is added that would slowly drag the whole thing down until the next Just Write Plain Text blog post.