I hate to be negative but I tried this a few years back, (not sure it the software has changed any or not) but it really doesn't work well.. With the combination of road noise, interior noise and wind noise (unless you car is like a coffin inside) it makes it almost impossible for the computer to recognize what you are saying. Then there is the HUGE amount of data the you have to load into memory for commands such as "PLAY Shakira-Oral Fixation, Volume 2 How Do You Do" ..
As for it being illegal for the displays to be in the line of sight of the driver, well how would we use the GPS systems? or Radio functions, as many car manufacturers are starting to use large touch screens instead of the old 2" radios.
But good luck with everything, and let use know how you make out..