Yeah I thought about this as well and is something I originally imagined as a cool feature.
The problem, though, is that not everyone will create a sub-layer for every component. It'd be a bad user experience for the viewer to have to just try clicking components to see which ones work, and I don't want to modify the look of the diagram, from what the author intended, to add some visual indicator that it's clickable.
Please do reconsider adding a visual indicator. Direct manipulation is a powerful UI technique and helps retain user focus. It could be something as simple as the mouse pointer changing when hovering over a component that can be drilled down into.
Hovering the navigation on the left could also highlight all linked components as well, giving a better sense of what you can drill into (without having to discover for yourself by moving your mouse all over the diagram).
The problem, though, is that not everyone will create a sub-layer for every component. It'd be a bad user experience for the viewer to have to just try clicking components to see which ones work, and I don't want to modify the look of the diagram, from what the author intended, to add some visual indicator that it's clickable.