Apps like classic notepad are useful to have around, when apps that try to parse things like markdown get it wrong and the underlying file needs to be fixed.
For example, a prompt when opening the file like: "It's unclear what kind of data this is, here are a few options with a preview, pick which one you'd like me to use."
Annoying, but them's the breaks when you're making software and aren't willing to put in hard requirements about what it is expected to (not) operate on.