I follow the car modding scene and to be honest, in the U.S. there don't seem to be anything preventing this from being street legal.
Even in California, something like this being a non-engine mod I don't see it being an issue.
The approval I got from the engineer was due to the following points:
1. The 6 speed came out of a newer generation of the model.
2. My controller has some safety features.
3. My controller emulates factory hydraulic behaviour. Had I implemented something like a transbrake, I would have been in for a very long ride of red tape.