Peter Sikking wrote some time ago (2012) an nice UX concept:
You did use the right word: concept 
It hasn’t been discussed much if nodes would be exposed in UI at all.
Also, back when I added ‘adjustment layers’ and ‘layer effects’ to the roadmap, I did so with the sole intention to use terminology that is familiar to Photoshop users.
It could be layers. It could be nodes. It could be both, in fact!
Do note though: exposing nodes UI suggests that the internal window system has to be updated/rewritten in GIMP (which is long overdue in my opinion). Right now, in the single-window mode, you have just one window visible at all times + dockable dialogs.
As soon as you bring node compositing, you need regular image window and the nodes compositing workplace visible at the same time. So at the very least you need to make dockable dialogs capable of attaching themselves to top/bottom and thus splitting the screen into image window and node compositing window + other docks. The reason being, when you have complex projects of dozens of layers, I don’t think you can get away with just the preview in the backdrop (Blender-style). You need to interact with the project in different ways.