Markdown support isn't a bad idea, actually, as long as they don't break the most important (IMO) property of Notepad: binary WYSIWYG. I.e. if I type in some plain text and then open the file with anything else (including after moving to another machine/platform, or even viewing raw data stream in transit or on drive), I can trust to see that text, as is, and nothing else. In particular, if I restrict myself to lower 127 bytes, I expect byte-to-byte correspondence.
(Modulo CR/LF, of course.)
Notepad being a plain text editor, it always supported markdown. Versions of notepad from the 80s would be able to open and edit markdown, as it’s just plain text.
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.
FWIW, Notepad has had support for BoM detection and wide-characters (UTF-16/UCS-16) for some while. That said, IMO, most simple editors at this point should default to UTF-8 encoding and only LF for line endings.