I've got a combination of loop/clicks, metronomes, and CoreSound Pads (20 minute loops) in my set. I don't know the best way to fade out of the loop without getting more hardware.
It'd be sweet to have a "Fade Out" button on Prime that pulls out of whatever track you're in; that'd work great for ambient pad loops. How does everyone else fade out? I'm clueless, though I've considered my Ernie Ball volume between the iPad and DI.