All the basic file operations (Create, delete, move by drag and drop, etc...) would be great.

Well Myako, what I tried to say is that when talking about edit books (ePub as a compressed group of xhtml files) we are talking about edit 'prosa' but we are also speaking about transform plain text to XHTML files. So I think MD and MMD are simply the perfect way to do this.
Would be great to do that.

It would be great. Something simple using Markdown or Multimarkdown to preserve the minimalistic layout but being useful as a text editor or a code editor at the same time.