Sounds good, that would have been my main concern, but apparently the system is sufficiently robust to 'survive' a lost I2C connection to the display. Kudos to BMW engineers (I've never been a fan of the brand's image, but I gotta hand it to them when it comes to engineering - although my gf's Mini is a f*** b*** when it comes to its crappy VANOS system, but that's a whole different story).
As long as the Arduino and the radio operate at the same voltage (or at least within reasonable limits; let's say <300mV difference) I think you should be able to get away with some CMOS switches. Does the display stuff run on 3.3V or 5V? Make sure you're powering and controlling the display at the same voltage on both the radio and the Arduino side; it'll prevent problems in that area.
I assume you are using a resistor voltage divider to read the iBus stuff that's natively 12V, but that's a different matter than the display part.