From what I understand, you’d like to be able to create a hierarchical relationship between concept-notes (hierarchization) and to be able to display the hierarchy in a certain way (visualization).
The way this could work is by using tags for the levels of the hierarchy.
eg
#lvl1 – person
#lvl2 – doctor
#lvl3 – pediatrician
#lvl4 – pediatric oncologist
Someone else might use the structure differently.
eg
#lvl1 – the 20%, the most important, highest-leverage notes
#lvl2+ – the 80%
With the hierarchy established, there could be different ways of visualizing the structure (eg radial, stratified, etc). You might choose to visualize your system in the way you described it (I didn’t understand it very well). Someone else might use a different visualization method.
For instance, in terms of visualization, I’d like to be able to control what notes are displayed in the foreground (#lvl1) and which in the background (#lvl2+).