I've wanted to do this for a long time to every window in every car and house and building.
The first time I saw it was on This Old House.
With my projects I did the last couple of years I have been researching this and other technologies like it. You can have multiple options. You can do the smoke. You can do black. Or you can even so one that is adjustable. The only problem is you would basically have to remake every piece of glass to put the sheets inside. Then you have to deal with moisture. The examples I've seen in houses sometimes stop working properly because of moisture. Also, they work backwards from what you may think. When you turn them "on", meaning there is power going through it, it will be clear. When you turn them "off", there is no power going through it and it will be black or smoked or whatever one you have.
But it is one of the coolest things. I swear a fairly recent Ferrari had this on the glass roof that you could remove. Anyone know what I'm talking about?