Here's a little vision for the next (ok, maybe next after that) release:
Audiobus will have two modes/panels: there will be a simple connection panel and an advanced one.
The simple is like today's with (more than) three inputs, one insert effect and one output. Simple and clean.
The advanced is where the real magic happens. There you can have multiple inputs just like in the simple panel, but where the routing gets a lot more advanced. There can be send effects that can take more than one input, and there can be any number of insert effects, as many as each effect app can handle in parallel. Each effect app would need to be able to expose multiple effects to AB for being used as input effects, as ios won't allow for multiple instances of each effect app. The insert effects can be routed in serial or parallel, and also fed to send effects. The possibilities would be endless. Heck, you could even create feedback loops if you wanted! When registering an effect app the developer specifies if it's a send effect, an insert or both.
The outputs in AB could be both effect returns and track inputs, or anything else of course that can take audio as input (side chaining a compressor for example). Yes, MULTIPLE outputs.
You can save routing schemes, add favorites, share them with others and what not.
Audiobus would automatically sync all effects and apps included and own the master clock.
There would be performance parameters that would enable low end iPads to cope with all this, for example by using high buffer sizes, smart latency compensation and lo-fi and sub 44.1kHz modes to allow for live performances or just to avoid stuttering. But there would also be a render mode that could render the audio chain in non real time for usage in freeze situations in a DAW. Audiobus Freeze.
What else? Oh! Inter-synth engine integration! Waveforms/samples/oscillators can be routed between apps. The Audio Engine Bus. Same thing goes for effects and filters... Keyboard splits between different AB inputs. Modulation sources in other apps..