I’m not at all sure about this new “Gutenberg” editor they’re adding to WordPress. I’ve installed the plugin version to try it out. Gutenberg is a change to the web-based editor in the WordPress dashboard, not a separate app. I typed up my previous post in MarsEdit, as is my wont, and uploaded it. The Gutenberg plugin imported it nicely and displayed everything as you’d expect. But it turned all my Markdown into HTML.
That’s not what I want, and it’s not how most Markdown-processing plugins — notably WordPress’s own Jetpack — handle Markdown. Instead they keep the source document as Markdown and only convert it to HTML when the page is requested. That’s what using a dynamic CMS means, after all.
It appears that you can get Gutenberg to keep the Markdown as it is, if you type it into what they call a Code Block. So I’ll have to hope that @danielpunkass updates MarsEdit to send posts to that kind of block once Gutenberg is the default. Assuming the WordPress API lets you do that, of course.