Has any blogging platform implemented anything like that? I know there are Markdown editors with a split view, but I don't know of any that are web-based, nor any that are integrated into existing blogging platforms. And I've definitely never seen any "manage/edit old posts" system as clean and simple as the one in the concept.
Oh, and btw, a brilliant concept that's super easy to miss - being able to type "(image)" in the editor pane and seeing an image upload placeholder in the preview pane. It's a small thing, but one of those things that seems way more obvious than it actually is.
I'd love something like the "Oblivion" colours in gedit for instance, although I am aware that opinions differ on dark backgrounds :) It would give a nice visual distinction though, like the old "underwater" mode in WordPerfect.
It keeps position as you scroll and write.