Early this morning the @AudiobusApp Twitter account revealed two interesting links! Developers from WaveMachine Labs, makers of Auria, and Sonosaurus, Thumb/DrumJam, have stated they're working on implementing Audiobus.
Rim, WaveMachine Labs in a thread on Audiobus' approval by Apple.
Sonosaurus developer Jesse in a thread requesting Audiobus support in DrumJam.
Neither have said if they will be available at launch, when Audiobus is released officially. I can confirm they are both on the short list of developers with early access to the SDK.