FoldingText isn't really a "minimalistic live Markdown focus mode" app, it's a productivity app, closer to something like Emacs' org-mode. I have no doubt that org-mode is more powerful, if you're already living in Emacs. (I can use Emacs, but I just can't get into it as a way of life.)

But FT isn't really being actively developed anymore, AFAICT. The developer switched from working on TaskPaper to FoldingText and then switched back to TaskPaper. Before TaskPaper he was working on WriteRoom, which was a minimal Markdown app, and sometimes it comes back and sometimes it doesn't. TaskPaper is pretty neat, but when push comes to shove it could be implemented as an extension/package for nearly any competent text editor. (And in fact has for several, including Atom. Folding Text also existed as a plugin for Atom at one point.)