This is ludicrous.
Apple has licensed Airplay for audio equipment for years and it hasn’t caught on with 3rd Party Manufacturers. (I’m not knocking it, I love AirPlay and is it all the time, but only with Apple products. Apple TV’s, Airport Expresses and the like.) Airplay hasn’t caught on because of the licensing. Bluetooth is ubiquitous no matter whether one is using Android or iOS, Windows or MacOS, everything works with Bluetooth. Why would Sony, Sennheiser, Philips, AudioTechnica and all the other headphone makers invest money into licensing AirPlay, just to be compatible with Apple products, that while popular, are not dominant in market share. They’ve already got Bluetooth!
You’re ignoring the fact that the Bluetooth 5.0 spec was announced months ago, boasting 4x the range and 2x the speed and huge gains in energy efficiency. Compatible chips and software are expected to hit the market beginning in Fall 2016. Even if the iPhone 7 misses out on the new tech, the next one won’t. I could imagine Apple introducing new lines of BT 5.0 Beats headphones to coincide with it’s adoption on the iPhone and other products in 2017.
I believe that this phone will be a transitional phase. No analog jack, but it will have a free wired adapter. The next one may not include a free adapter if it has Bluetooth 5.0 and the Bluetooth headphone market is in good shape next year. They will slowly push people towards Bluetooth wireless headphones over the next 2–3 years.
All that isn’t to say that they couldn’t utilize AirPlay on their own products though. What if the next generation wireless Beats headphones had AirPlay functionality, allowing one device to broadcast an audio stream to multiple headsets? They could build an entire marketing campaign around sharing music with friends everywhere you go. On the bus, on a plane, at the library, etc. There could be a simple, Apple-y configuration where one plugs the headphones into a Mac/iOS device to name it and set up preferences, then it would also charge up through Lightning cables.
I’m not enough of a techie to know for sure though, but I believe that AirPlay is dependent upon a network. That’s where Bluetooth is different. It is device to device, directly. AirPlay is device to device via an existing network. So, I’m not sure what you’re talking about (or even my own idea) is technically possible right now with AirPlay.