Smart mirror for your car

This idea came to me a long time ago. I imagined a digital rearview that would turn semi transparent when dimmed. No need to adjust. It's like when you have sunglasses for the mirror, but they adjust, and the mirror is digital. Not sure why it's not out yet. To me it makes more sense than a complete mirror or just a plain looking mirror. Any bells?<br><br>Edit: I have a set of tinted glass sunshade screens that I use on my mirrors. The rear one is pretty effective. They're cheap and I'm sure easy to produce. I complain about most tech because it's ridiculously priced. I know a lot of people are familiar with this product, and they're widely available. It's not a huge innovation, but it's something I wouldn't use my car without.