Ok, i know this is all too many long posts, but one more thought to add...
it also occurs to me (re percussion looping), that i would be useful
to incorporate MIDI looping along with the audio looping, because the
possibilities for automated variance are so vast (I used to hate
working with midi sounds, and only preferred to manipulate sampled
audio, but these days midi sounds are soooo much better than they were
10 years ago).