Some cars already have this, for sound isolation… including the model 3 and model S. I’ve had some cars in the past with this feature as well. It is relatively common.
True, although with double glazing you can probably make the HVAC unit smaller, saving weight there too.
And you might not need air vents to defog the screen either - a well insulated window won't get condensation on it to start with.
And double glazing typically needn't be much thicker than single glazing - as long as the air gap between the panels is sealed, then the air itself gives the whole window dynamic rigidity. That's why you sometimes see a thief throw a brick at a double glazed window and it doesn't break.
That should give reduce the energy used for cabin heating, reducing range loss, perhaps by half for longer journeys.