I've been working through my Owner's Manual (internet version) and a front camera is referenced in the "Sensors of the vehicle" section. It is used to read lane markings for Lane Departure Warning and speed limit and other signs along the road to display the speed limit in the cluster. But I've got no idea whether the video capture module is included in my Z4.
It's a cool feature that I would definitely get. It might be that the convertible models don't have the space to wire it. Once I get set up in ConnectedDrive I'll put my VIN in and see if they offer it to me. I've got the Executive Package and Active Cruise so if it's available for the Z4 it ought to work in mine.