This is slightly off-topic, since my problem is about rearranging a linear order and not necessarily connected to trees.

Of course I knew this article already, it deals with structure which can be described as hashes of hashes.

But my f_sort expands the model to also include arrays.

Please note that the described downsides are rather obsolete for trees with a maximal depth, as long as you can use Self Joins and Updatable Views.

And even a dynamic depth could be handled by redefining the view.