How hardy is TaiTri?
I can't comment about TaiTri, but can share this about Taiwanica.
On April 5 (2019 ) I talked to Nat Bradford. He used to live in Seneca, South Carolina, which he insisted is zone 7a. (I'm looking at a USDA hardiness map and Seneca appears to be listed as being on the border of zone 8a/7b though, but I pressed him on this point at he was adamant that the location was definitely not in zone 8 )
He said he grew a Taiwanica lemon and an C. ichangensis outside there unprotected, and they have survived for 7 years. At one point he says the temperature got down to 4 °F. He says his Taiwanica lemon survived all this time. I specifically asked if it had survived the freeze in 2017-2018, and he said yes, he had gone back to the property and saw the tree was still there, even though he doesn't live there anymore. The Taiwanica was grown from a seedling and is not grafted. He initially grew them in one gallon pots and left them outside, they survived. Then he eventually planted them out into the ground.
The C. ichangensis has lost leaves and the leaves have turned yellow-brown every Winter, but he says the Taiwanica did not lose leaves.
I was very surprised to hear this.
His Tiwanica has fruited, but he says his C. ichangensis never set flowers.
I also asked how his hardy citrus hybridization attempts have been going, and he said he's been busy and has a few seedlings from his Taiwanica, but nothing else besides that.
This is the same Nat Bradford whose name is connected to the Bradford watermelon, once a famous heirloom variety in the South, and he did an internship at Longwood Gardens in Pennsylvania.
Since TaiTri is a hybrid between Taiwanica and trifoliate, I think we can assume this implies something about its hardiness.