hey, Pushcut developer here.
thanks for this detailed post, there is a lot of good information in there!
the main issue in this case for Pushcut is that pretty much all of the techniques you listed require the app to “run”. for iBeacon-based background/location triggers you need to hand off everything to iOS, with basically zero configuration possibility. iOS decides when you are close enough to “enter”, and when you have “left”.
this is obviously for very good reasons (you do not want every app do its own beacon ranging in the background) but comes with these drawbacks…
you can do a tiny bit of background processing once iOS tells you are close, but you might get killed whenever iOS feels like it. so the possibility to measure signal strength until you are in a certain range cannot really be done reliably…
WWDC is going on right now, I’ll be checking if there are new OS features coming to consider here ; )