Hello @bubbavox,
I had come to the same need. So, this is a feature that I integrated into OpenCutList extension.
I confirm that it’s useful to have the materials displayed in the structure tree.
Even if, as @curic4su says, the faces are still missing in this tree.
It’s not so easy to replicate all the outliner’s features. But you can already try what I did in the beta version of OpenCutList 7.