None of the documents that I write for myself and much less any of the documents that I write for others could be written as .md.

The reason is that I always use only good typefaces and I must use various typeface features provided by the OTF format, to which something like .md does not provide access.

If .md would be extended with the missing capabilities, then it is likely that it would become not much simpler than ODF.

Even in the simplest documents that I write for myself, I must use multiple document styles, as provided by a format like ODF, because I typically mix multiple languages, including multiple alphabets.

.md is OK for a ReadMe file written in English, but it is not good enough for what I would call a real text document.