2 votes so far Windows WASAPI Loopback, I doubt there’s going to be any progress made here.
In the meantime I’m trying to implement it with miniaudio library with moderate success. Got the loopback working. But stopping and opening a new device ends up in an infinite “wait for an object” loop. I reckon it might be conflicting with what’s going on with JUCE’s WASAPI back end at that moment.