If you need to display HTML content (what Markdown usually translates to) then WKWebView is the control to use! Or use something like litehtml which should be more than enough for Markdown unless you want to support "Animated Gifs" (that are actually H.264 movies these days) or whatever else.

You can still use native controls for the rest of the UI and have 0 Javascript running. I'm not sure I understand what the problem with NSTextView was though. It's pretty performant as far as I can tell?