You only need the rear view for keeping an eye on traffic behind while on the road, so basically the window should be the size of the FoV in your rear view mirror.

For parking, I don't think I have looked at anything but cameras for the last 15 years. The camera is so much better than both looking backwards and using the center mirror. Especially with 360 cameras because you can then "look" backwards without missing anything happening elsewhere. I definitely bought my last car without 360 cameras several years ago.

And kids running behind the car when reversing. Honestly, visibility is in the top five criteria for me (others include driver's seat, sound proofing and big boot lid). Parking sensors and cameras of course help but are they a total substitute?

The kids case is one where camera has a clear benefit I'd say. Even if you have clear visibility to the rear window, you just can't see anything below the window height. And anyone coming from the sides you'd not see through the rear window either - but a very open vehicle might be a tad better through the side windows? Although with cameras being added to side mirrors or vehicle corners (and large screens!), that can also be expanded.

A good reason to have the windows down when reversing - at least then you have the benefit of hearing any kids behind you as well.

Total substitute. And they have to be, because once you have them you ONLY look at the screen. There is no chance I'm even glancing in the useless top mirror, nor over my shoulder. I do switch between rear camera and 360 camera though, but it varies between car brands if that's necessary. In the best implementations you see both at the same time.

Well the new Polestar solved the problem… by removing the rear window altogether and slapping a camera in its place. Not joking, look it up!

How the fuck is that even road legal?

There's plenty of vans that don't have any rear windows

My campervan (Promaster 2500) has rear windows, but it isn't like I can see anything out of them when I'm driving. Usually just leave them covered anyway.

I've only ever heard of a requirement for 2 mirrors. Those can be on the outside.

Varies by state in the us. Some require two mirrors and one must be outside on the left. Some are similar but on the right. Some states you need two outside if the one inside is blocked.

because you can see what's behind you? Via the camera, but that'd just a detail.

I've had plenty of car cameras glitch out or stop working.

To say nothing of getting crusted with road salt anytime you drive in winter.

I said that it's possible to get better. Not inevitable.

This is the Polestar 4 without the actual rear window https://uk.motor1.com/news/663436/why-polestar-4-has-no-rear...

Aside, IDK if the Polestar 4 is "the new Polestar".

The Polestar 2 is on the roads - I've seen them, and the 3 hasn't even shipped yet, now due in 2024: https://electrek.co/2023/05/11/polestar-delays-polestar-3-pr...

What does that make the 4?