Same boat. I have been using WordPad and .rtf format for all my notes for maybe 15 years.

I've been meaning to jump to a markdown editor for a long time, and after this news I've already started using MarkText. I probably should have jumped ship a long time ago, but at least I'm on the path now.

I will have to figure out a neat way to convert my .rtf notes to .md. Update: I've found Pandoc, it's a command line tool for which I've made a script for converting my .rtf files to .md.