I agree, its an idea I've been playing with for a while also. The difficult part would be isolating the sound, but perhaps with new ai audio models that has become trivial, its definitely worth revisiting
You can also probably guide a user through a couple of system changes to isolate sounds. For instance, a sound related to the alternator may change with both RPMs and electrical load. A sound related to the serpentine belt might be affected by engaging/disengaging a mechanical load like the A/C. A wheel bearing or brake noise will track with the rolling speed, not the RPMs, and may be affected by steering (a hard turn to the right may unload the left side of the vehicle.)
I'm blown away by how much diagnostic info a good repair tech can get just from listening to a car; I would pay to have this kind of guidance in a phone app.