I like the idea.
I suggest doing this by mouseover: If i hover with the mouse over the device “BlackDS”:
or if i hover over the folder “Kay”: i can quickly see where my folders are shared, too.
I think this is very useful to quickly check, which nodes will be anounced by the introducer functionallity. (because, as far as i understand, the only the devices which share the same folder are announced over the introducer)
I can even imagine a button next to the introducer - checkbox: “Show the introduced nodes” Which then highlights all the devices introduced, while everything else becomes darker.