First of all, congratulation for pulling off a new and experimental user interface!
However, I believe, the idea that tree- or graph-like structuring of text is beneficial for reading and writing text in general, comes close to the graphical programming fallacy. Eventually, the spatial make-up fails because of the following three reasons:
(1) The manual difficulty of navigation and the count of subconscious visual cues necessary for retrieving a passage increase exponentionally as the content grows, (2) altough thoughts do seem to come in hierarchical structures, we usually don’t think of text, code, stories, memories nor knowledge as visual graphs and (3) textual hints for emphasizing and linking text are more efficient and flexible than visual hints.
At first glance, Wikipedia seems like an affirmative example for graph-like structured text, but that structure is usually not used for primarily intended navigation. The articles are actually expected to be self-contained for readers with only a fair amount of prior knowledge.