Official retrofit is out
https://service.tesla.com/docs/Serv...Rear_Touchscreen_Bluetooth_Audio_Retrofit.pdf
They actually do mention a gateway change (“frontUsbHubType” to 1), but I double checked my 2023 car (which came with the rear bluetooth), and mine has that set to 0. I might try changing it and see if anything changes.
Edit: So other than changing the description from "2" to "2_BT", there doesn't seem to be a functional change. And since cars with this from the factory have that config item set "wrong", I don't think there will be any real issue for anyone who DIY'd the retrofit.