I've been playing around today with the suggestions above. Maybe I'm doing something wrong but I can't get 'sound on sound' looping using these techniques.
The problem seems to be that every time the sequencer loops around, the audio recorded on the previous 'pass' is erased. There is no way to retain the audio in the track recorder.
With manual sampling this is OK, but you can't really do manual sampling while playing an instrument at the same time. 'One Shot' recorder trigs aren't really the answer for me either.
I think the fact Elektron are looking at implementing a dedicated LooperMachine is an acknowledgement that, in its current form, the OT isn't set-up for traditional 'looping' duties.
I'm sure a dedicated LooperMachine will be better than any other looper out there though - it'll be an Elektron take on the concept.
I'd love to think they will bring out a footpedal for the OT too. They probably wont, but I can dream!