I'd love to see a sound system a la Jack or even Pulseaudio compared to Android's native sound system, though do recognize that at least for phones there are challenges, as of course you need to kill other sounds to accept an incoming phone call. Routing multiple outputs would be handy -- perhaps to keep some background music on while working played through a Bluetooth speaker, but then maintaining the ability to take phone calls either on the phone, or perhaps a Bluetooth headset without interrupting that music stream. Just because most people don't want more than one application outputting audio at the same time doesn't mean we shouldn't have it as an option. And I'm sure some would also find utility in handling multiple inputs as well, without relying on a discrete hardware mixer.