That obviously seems insane, but it would explain why the "razzlequat" or Eremolemon grows outside in Southern Oregon at the house that used to belong to the Oregon Exotics Nursery owners. It's zone 8a, gets into the low teens regularly in winter.
Um, I hate to burst your bubble, but I've talked to the owner of Cistus nursery, which is on a fairly big island right along the river in Portland, right outside the city, the outlying area and the island is pretty rural, and he's told me that a Satsuma mandarin has survived outside in the ground for him and fruited. This is in climate zone 8a, more likely 8b because his location is right in proximity to the river, on all sides.
(And it's also worth pointing out it probably gets a lot of shelter from the wind because the nursery is a virtual jungle, with densely planted shrubs and tall plants everywhere)
Jim VH (member in this forum) also observed that his Early St Ann Satsuma (had grown into a big size) survived unprotected this winter (the first time it was left unprotected) in his residential suburban neighborhood just north of Portland in Vancouver, WA, and probably would have fruited from the looks of it, but he chopped it down and took the tree out in March.
I know Southern Oregon can maybe get a very tiny bit colder in the winter, but the fact that a Razzlequat was able to survive there is not really a
huge demonstration of its hardiness. (Also the coast of Southern Oregon is a whole different story, some people say they can grow Meyer lemons there)
I'm sure Razzlequat is hardier than Satsuma, of course.
This is entirely from memory, so this could be totally wrong, and I am definitely not certain of this, but I remember from prior research I did, looking at people's reports in other forums, I strongly came away with the impression that Australian Desert Lime probably had around the same level of cold hardiness as Satsuma mandarins, perhaps a little more or a little less. I also remember looking up the climate zone information about where Australian Desert lime in indigenous to (which is certainly no clear indication either, usually citrus species can survive a bit more cold than the part of the world they came from).
It's probably worth looking into and doing more trials, but I highly doubt Desert Lime is close to being in the same league as species like Ichang papeda.
That being said, one of the notable things about Australian Desert Lime is its drought tolerance, it can probably survive better through periods of little water and hot dry conditions than any other citrus species.
(I'm thinking this attribute could possibly make its hybrids useful for low-maintenance ornamentals in public areas)
I would also guess that even if it did survive through a low temperature point, that period of time was very short. The conditions in deserts tend to be very different from temperate places further north. Due to lack of moisture or any nearby bodies of water to moderate temperature, it is easier for there to be sudden temperature swings. There's a big difference between going down to -11 F for just 20 or 30 minutes, versus going down to -11 F amidst a 24-hour period where the temperatures have remained well below freezing.
Maybe it is capable of surviving -11 F but suffers extensive damage at that point and is then later is able to quickly regrow and recover.
This post is mostly speculation, of course, I don't grow Desert Lime or Razzlequat, and I really don't know.
Good post, by the way.