In answer to your question, Yes BMW does offer over the over the air TV option in the M3, however this is offered in markets outside the USA. The TV option is nicely integrated into I-Drive and allows the video to be overlayed within a I-Drive screen. The TV option can receive both analog and digital European signals.
Although it might be possible to retrofit the TV option in USA vehicles (as far as I know, no-one has done this yet), there are a number of problems.
The first being, the vehicle would need to be coded to recognise the TV tuner. As far as I know, the BMW NA dealer coding computer is unable to do this.
Secondly, BMW would need to offer a retrofit wiring harness for the Tuner and antenna, again as far as I know this is not available.
And finally even if you could overcome the first two problem ... the TV tuner would probably only work with analog channels, as the tuner is unable to pick up USA ATSC digital channels. Therefore, its wont be long before those analog USA channels are switched off ... making the TV tuner useless in the USA.