Almost all old digital delays used to do this HOLD function, and my Roland SPE1000 was sort f the first digital looping thing i had (before that it was the classic 2 Revoxes)
..what would REALLY help in this context tho wold be to loop that oooh 100 milisecs first forwards, then at the end do a reverse, then a fprward, then a reverse.. that way there would be less bumps... wonder if something like THAT exists....
Course i can do it on a EDP, with midi control, and sure Mobius could too,, ... but a one button hit...foor down, its holds? Hmm twicky...