When you loop a sample you mostly have to cut whatever is after the loop, because it’s never played. That’s too bad, bacause often it can be for example some nice fadeout, which you can’t achieve with any simple envelope etc. So why not adding a “sustain sample loop” feature, so when the note is on, the sample is played looped. When a note off is sent, the sample plays to it’s end.
I think sustain loop in IT was used in the envelopes. You were able to loop an envelope during the note-sustain. I’m not talking here about this feature. I want a sample loop sustained, not the envelope.