Can we get multiple columns in which we can vertically accumulate short thoughts that can together become a writing section or even a chapter? A good implementation of this is at https://www.speare.com Have a look and you can get a fully functional 14-day trial. It is a neat implementation, but only web app, and no bidirectional linking.
Something like this is already possible in Workflowy using Boards. It would make it possible to go from an outline view to a full-fledged document view. But the main benefit here is to capture brief thoughts in columns that are related.
My use-case would be to build a database of thoughts and to be able to write by grouping previous thoughts together etc.