This tool is great, it's really versatile. I would love to see the mutator handle waveform offsets. Something I do often is shift the waveform offset in 45-unit increments, so I can quickly export 8 subtle variants without altering how it behaves.
Another big feature I'd love to see is being able to use WAVs as custom waveforms, like how the SNES could use looping and one-shot samples. It'd open the tool up for even more classic sound design.