I would wait because the idrive is now a major component of the car not just some flashy toy, so think of it as if the car was set to get a change in its engines. You wouldn't buy the car knowing the engine was being changed in a few months...
I would wait. In fact, I would actually wait for the all new 5 series if possible. Get a used honda accord which is a great beater for a good price until the new 5 series is out