The broadcast era put all the instruments on the speaker: message, channel, platform, reach. The listener was a receiver at best and a target at worst. The next move flips the symmetry. The listener is the sensor — the primary instrument for reading what's actually in the air.
This isn't a sentimental reversal ("audiences matter"). It's a structural one. When the listener is the sensor, discovery stops meaning "what should I say" and starts meaning "what can I read." Research, attention, positioning — all of them get rebuilt from the other side.