features I like in a looper are
iterative 'fading' of previous loops
chopping and reversing of the buffer
An open feedback path (for insertion of effects)
When using loopers to perform music the crucial feature is fade, the fading out of the old loops to give audio space for the new ones. Because of the immediate nature of looping live it is important to have a automatic facility to place older passes increasingly further back in the mix. On my old looper I had the control 'touch' which used stereo trickery to help out here.
Another element that people like is layers, I use Live effect racks with a chain select to route the incoming audio into one of 3 loopers or to bypass them. There's an image below to illustrate what i mean.
I also like to use loopers for studio re-synthesis, it is possible to create really interesting sounds by reprocessing audio on each pass. Using devices in the feedback path which enhance or produce harmonics means sound shaping is possible in a real 'hands-on' way.
My newer looper has a 're-trigger' which jumps the buffer read index to on-beat areas in the buffer. These jumps are written as audio back to the buffer and so are repeated. This is like a manually triggered beatRepeat. If I I am looping a drum loop and stab '3' four times quickly I will most likely get 3 snare drums extracted and then re-added into the loop.
Although I really like the idea of the looper being integrated into the clip / wave functionality, I am not sure if it would be possible to provide the crucial features such as fade, re-synthesis, etc. In addition - the performance GUI which is part of a Looper might sit uneasily with the currently cramped slip control area.
perhaps the overdub in clips must be a separate feature?
the looper I am currently using is this one I made myself - which is thrown together really, it is constantly in flux and a bit ugly.
there is a modulating delay in the feedback path.
You can also see the retrigger buttons at the bottom, I should probably use a 'map key-range to re-trigger start position' instead of 8 fixed buttons
I use 3 of these in a rack, like this :
the chain select will send my incoming instrument audio to one of the three loopers, 4 bar 8 bar or 16 bar (or bypass/clean).
This is my standard looping setup for just noodling ambiently