I'm not understanding why Markdown would deprecate TinyMCE. Markdown is markup, and seemingly more appropriate for the plain text editor. TinyMCE is a visual editor that shows WISYWIG.

I could see Markdown markup replacing the HTML markup for the TinyMCE buttons, but the TinyMCE editor would still show WISYWIG.

It's just not making sense to me. Markdown and HTML are tools for us geeks. WISYWIG editors provide a needed abstraction layer for the vast majority of people who have no need or desire to learn either HTML or Markdown, and just want to write formatted content.