Thanks again for the insights. I may look into using the iConnectivity hardware at some point (and you’ve been really clear about the caveats, thanks for that!), although what I’m really trying to do is simplify my setup and breakdown, and managing two devices instead of one seems like going in the wrong direction. 
I have not yet looked into the Enso looper, but I will do that–thanks for the recommendation.
Did you say there is a QuantiLoop available for Mac? I’ve not seen that before, certainly not at the main website; where are you seeing it? I’d deal with it in standalone, for sure!
It’s a fair question to ask what it is I like so much about QuantiLoop, and really I can distill it down to the two features that separate it from anything else I’ve seen thus far: 1) it’s a four-track looper (four seems to be enough for me), and 2) it also carries a feature that is critical for me: loop overdub decay.
I have not found this combination of features in either a hardware or software looper that is not exorbitantly expensive. So, for example, on the software side, I’ve heard of Ableton Live being able to do this, but I’m not invested in that landscape. It’s theoretically possible that the old SooperLooper VST might be able to do it, but I’ve never seemed to be able to get that running. Every now and then I check in on currently available looping apps for Mac, and there are usually several that seem very well featured except for the overdub decay problem, which again is a deal-breaker for me.
On the hardware side, my first taste of overdub decay goodness was via the TC Electronic Ditto X4, which I have and absolutely love, but it’s not a small pedal, and even it “only” has two tracks (where QL’s third and fourth tracks are sometimes very nice to have). The other one I actually have, Pigtronix’ Infinity 2 looper, is a bit more limited than the Ditto X4, but it’s much smaller, still has two available loops (albeit series only) and overdub decay, and is very affordable for what it does.
There aren’t many other hardware looper options in this specific space, somewhat to my surprise. Pigtronix has the Infinity 3 now, but it’s bigger and spendier than the 2, and doesn’t really do any more of what I want. EHX is in the space with a couple of its loopers, and actually has gotten closest to QuantiLoop with the 45000 four-track hardware looper with overdub decay, but that’s both big and expensive. (And the EHX is a better configuration than the similarly-expensive Aeros Loop Station, in that the 45000 is intended for the tabletop with a support footswitch, while the Aeros is designed as a floor pedal that can be supported by a MIDI control surface on the table.) Other than that, I’m just not aware of other good options–although I’m always open to being further educated!
And so against all that, there is QuantiLoop, fitting neatly into an Audiobus scene along with MG2, TONEX, and other apps that I can use on iPad…with its four tracks, overdub decay, and preset switching. Via a compact MIDI control surface I already have on the tabletop (Korg nanoKONTROL), I can manage its tracks and overdub decay level without bending over; and via a compact MIDI controller I already have at my feet (XSONIC Airstep) I can assign it a single footswitch (or more of course, if I want) to rec-dub-play-undo-redo-stop-clear whatever I need to do with my foot.
If such is possible for Mac, and is affordable to the perpetually broke, I’d love to hear about it. Until then, the idea of steering toward iOS is persistently attractive. 