It appears that the retrofit kit is available in Europe so I guess we are just waiting for BMW NA to release it.
I imagine that NA will do their own tests and re-write the installation instructions to suit US models and environment, as is usually the case. The instructions I attached earlier came from a UK BMW dealer.
The individual parts of the kit are almost certainly available in the US as regular spare parts with two exceptions, those being the USB retrofit harness and, for cars without Bluetooth or phone prep, the retrofit power cable. I ordered a USB hub and a USB/Aux-In jack in the US and those arrived ok.