A good think with Markdown is that learning can be incremental: at first, you just write some text. Later, with the preview, or with a short guide always displayed under the textarea, you learn that you can do some formatting.
On the other hand, people using WYSIWYG will go the other way: the will first see they can do a lot of stuff, and later get confused when stuff does not behave in the expected way.
In fact I am using that, but with a different Markdown blogging plattform. ;o)
I heard Atom.io already does that, but I haven't been able to get it running on my laptop, and npm just keeps littering my filesystem with its `node_modules' directories.