Plain text is not inferior in literally every way. It's superior in not needing additional tools to understand. Not no tools, but a bare minimum which cannot be said for pdf.

True that formatting and images and other niceties are not in txt. But when the core question is "how to preserve the text" (not "how to preserve this specific prettified version of it"), then txt is superior.

Personally, I currently would advocate for markdown. All the advantages of .txt as it appears on disk, and some basic formatting understandable by parsers without requiring such formatting to be understood