Do you mean you want something which outputs audio in the same way the virtual camera outputs video? You mentioned capturing audio, but then compared the feature to the virtual cam which is output only.
Both capture and output features would useful (Windows version of OBS already captures desktop audio without additional programs, would be nice to have that in the Mac version but there are plenty of workarounds for the moment), but an audio feed to pair with the virtual camera would be especially handy when webcam input is required.
I know this is a featrue request, not a help request, but if you want something in the interim you can use vb-cable/blackhole as your monitoring output in OBS, then pick up that feed in whichever application you want to receive the audio. If you need to monitor the output, Windows, Mac and Linux all have ways of listening to or aggregating audio inputs/outputs.