editor-style.css is great, and surprisingly easy to implement. I've even got it to reflect changes made in the Customizer and the page template. There's really no excuse for theme developers to ignore it. It's possible to get near 100% WYSIWYG, apart from shortcodes and the fact some content is represented by a placeholder. The only issue I've had is images with captions, which are trickier due to the different markup in the editor.

The fact that Markdown keeps coming up as a suggestion for WordPress just shows me how insular the development community can be. They really need to expose themselves to the average non-technical users. They'd realise that Markdown is a laughable suggestion for improving the editing experience.