i’ve created a similar thing – called it “page designer”.
sneak preview: http://recordit.co/udTPhnSBVe
in fact, its a flexible layout in a row-repeater field.
it’s build on the bootstrap framework and you only can add one sub-level.
to add modules, you just have to add an folder in the theme directory and also create a view.
So no huuuuge flexible-fields madness in the backend. 🙂
at the moment it’s not open source but in a private repo. depending on elliot’s future plans on this topic maybe i should make it public.