The AirPlay audio streaming technology is based on old protocols reaching back into the AirTunes days … it needs a revamp. The official Apple answer is to buy your own speakers and hook up an AirPort Express which is both clunky and prohibitively expensive.
The success of portable Bluetooth speakers says to me that there is a consumer desire for wireless music streaming in the home. I think Apple should re-engineer AirPlay as a WiFi protocol that requires an internet connection. This means it could also sync up with HomeKit and be controlled remotely, outside of the home network. Essentially, each AirPlay receiver would stream music from an iCloud / Apple Music server. This means individual devices do not have to manage the streaming work locally. A friend could stream a playlist at your house and leave with his iPhone in his pocket without interrupting the music. It’s the Chromecast model.
Making things based around an internet model simplifies so much. Apple could do some really intelligent things, like automatically silence speakers when you leave home. Couple a reworked protocol with some pretty speakers and you’ve got something good.