I'm happy to see all of these creative approaches to optimizing
tree structures, which are really important in general (and
promise to become even more important in a lot of projects I'm
working on).
One thing that is often forgotten is that the bboard module uses
a hierarchy, with sort keys. It uses the simple property that once
an item is created, it rarely (if ever) changes position in the tree
structure. Thus, storing the sort key directly in the table is the
right way to go. Think of it as a "cached" sort key in a sense.
