The initial described problem (organising ideas in a hierarchical way) has already been solved efficiently years ago with visual mind maps. They have been used successfully to not only create the hierarchy, but also to realise that sometimes, the tree is more like a graph.
As a reader, it's infuriating to have to click all the time (or use keyboard) and have this page scrolling all around. I just want to READ, not being distracted by some kind of useless parallax effect.
As a writer, moving ideas around to get them properly organised is really painful. There is no distraction-free interface neither.
If you really want to make tool for writers, I would strongly suggest you that you take a look at tools like Ulysses or Scrivener and try to understand the rationale behind the UI choice they made.