The real trick with CS apps is to be able to chop off the live input at the 'Play' boundary. In other words, if you are still holding down the chord, as far as the CS app is concerned, it ends at the bar boundary.

A CS has a few significant differences to a sequencer. On the one hand, it's really only ever dealing with one channel's input (the NTA channel) and outputting one channel, but it has to do a little bit of housework to tidy up the input once the loop is determined. And with a CS, the loop length isn't decided until the users SAYS so! But I still don't see how it wouldn't be anything difficult for someone capable of a normal sequencing app.

I once tried to find out whether Ableton Live could be used, as it has a live audio looper, and MIDI capability, but I could never get a response from Tech Support or the forum. Anyone know a Live 'power user'?