If you're zone pushing and not gonna bring your plants indoors, consider starting many marginal plants from seed. And preferably from varieties that are confirmed or suspected to be most cold hardy. For example, if I were in zone 8a I would try and source as many seeds from avocado varieties Lila, Pancho, Joey, Fantastic and Wilma as possible, and making sure those seeds were not pollinated by any variety less hardy than those. The seedlings may end up being slightly more or less hardy than compared to the parent/s since they will have degrees of genetic variation, but this can come to your advantage. Not to mention, I have noticed seedlings often are simply more tolerant of the cold than their clonal parents. This might have to do with a stronger taproot, I can't say for sure just an observation. For example, this past winter it got to 24F and all 5 of my air layered lychee saplings (brewster sweetheart and mauritius) had major branch splitting, however out of the hundreds of seedling lychees I have lying around unprotected (from those very same varieties), most of them only had very small twig, leaf, and new growth damage. But there are many factors involved.. The seedlings may have simply been out of the wind and much closer to the ground, which near the surface of the ground a bit of contained Earth heat always trickles out, so maybe that heat was just enough to prevent major splitting on those seedlings.. I couldn't say definitively.
But even a little dinky greenhouse or cover will help out greatly. The same winter event stumped all of my in-ground annonas, but I had a couple pots with freshly germinated seedling atemoyas in a TINY greenhouse under some bamboo, and none of them were even phased.
And on the topic of stumping, you will want to prune your marginal plants HARD. The larger the caliper of trunk and branches the MUCH greater chance they have of pulling through a bad winter event. You want the least amount of fresher smooth wood and the most amount of thick bark as possible on all limbs. For example, the same past winter event (24F) re-stumped a few of my in-ground mangos. The mangos had already been stumped twice over 5 years by other bad freeze events, so they have pretty thick caliper stumps. All of their smaller caliper branches that had no real wood were burnt down. However, the few inches of stump that are clearly woody pulled through just fine, and are sprouting new growth (which I will be pruning hard to hopefully get woody too). Same concept as with some of my in-ground annonas..
Also I'd recommend putting those prunings to use by trying to root them up, grafting, or whatever. Might as well..
Some people claim grafting a less hardy variety onto a cold hardy rootstock will increase hardiness of the lesser by a few degrees..
You mentioned jaboticabas. My sabaras were fine at 24F, not even leaf drop on any. I assume they could perhaps be okay even a few degrees lower. No idea how the other jabo varieties would respond to that degree of cold.
There are obscure varieties of annonas from nothern argentina/south brazil and uruguay that will withstand -6C. a.sylvatica, a. emarginata, a. ubatubensis come to mind. There are others too.
There are many fairly cold hardy citrus and avocados if you were interested. Wampee, kei apple, white sapote may be candidates too. feijoa, loquat are bullet proof. surinam cherry also takes the cold, though a couple of mine defoliated around 24F, but no branch damage. Someone on this forum told me his Luc's garcinia and some other garcinias actually withstood below 20F with not much damage. 12-15F was his low. It would be resourceful to not have a bunch of cold hardy plants unnecessarily taking up space in a greenhouse.
You could experiment by rooting cuttings and seeing at exactly what temperature or conditions they defoliate/die/become stumped before subjecting a bigger or prized specimen to those conditions, if you know what I mean. The results may surprise you.. but then again could be misleading because larger woodier plants are often more cold hardy than something like a small experimental cutting anyway..
Also you can try and mound your plants with a bunch of leaves.
And one last thing. I accumulate giant mounds of coffee grounds and have noticed they get VERY hot even in winter. Even small mounds. (significantly hotter quicker than a typical leaf & wood chip pile) Like 150F+.. It would be resourceful to utilize this heat energy, under a tarp and frame or something. You could have a big mound with a sealed tarp over it and pile all your potted plants around the mound still under the tarp. Or have a tarp set up and drag big totes of composting grounds under the tarp with the plants if you don't want the mound of grounds sitting directly on the ground. Just go around town and ask the coffee shops to save their used grounds and start accumulating.