We already have what you see is what you MEAN
We do not.
“WYSIWYM (Typora-like)” would mean that you can type in Markdown and see the resulting formatting in a single pane, including seeing your attached images, mermaid graphs, or other content inline - depicted in way that is structured and formatted, but not necessarily design-accurate.
As of now, you currently have to switch between Edit and Preview modes, or have two panes open. That’s the fundamental problem being addressed in this thread.
WYSIWYG means that you’ll see an accurate depiction of a final rendered output on screen or print. This is not what this particular thread is asking for. Since you could have any arbitrary text-editing CSS theme to suit your tired late-night novel-writing eyes, but then export your final document(s) to any other type of CSS theme or YAML-formatted output to suit your editor’s manuscript needs, for example. Or your website’s funky typography. There’s no particular reason for the two to be the same.