It'd be nice to be able to play a sample from the beginning, and then have it loop to a point other than the beginning. This is a common feature of module/chiptune music formats like .xm and .it. In case that's not clear, I'm suggesting that you add a "loop" knob to the sampler ui.
Start knob - Sets the Starting Point of the sample
End knob - Sets the Ending Point of the sample
Loop knob - Sets the point to which the sample loops once it reaches the Ending Point, provided you have the "loop" option ticked.
It'd make the AudioFileProcessor so much more versatile, and would be a welcome familiar face to tracker uses who are accustomed to programs like FastTracker and OpenMPT.
Edit: For example, with this feature I would be able to turn a short one-shot sample of a piano note playing into a long sustained note by looping just a tiny section at the end of the sample and setting a long decay time in the volume envelope.