New is not yet forgotten old
In the 2003 and later BMW’s, (model specific), your rear window has integrated the AM aerial, the TV aerials, 4 FM aerials, the receiver aerial for the remote control, and the electric heater. This is addition to a aerial amplifier at the top and a special seal that insulates for improved sound.
We posted info regarding the research being done on the futuristic windshield. But, your rear window is already handling some pretty specific tasks. And all you have to do, is keep it clean.