Yes placing the cameras at the positions of the mirror faces rather than using them for dynamic reflections would allow for more realistic mirror reflections, since it would include the vehicle in the image, which is very helpful as it allows you to know how close your vehicle is to objects in the scene. And the cubemap reflections cannot include the car in the reflection, since the cubemaps are generated from the center of the vehicle, and would be obstructed by the car's interior. And because it requires less cameras (side mirrors, rearview mirror, and player's cam so 4 total) than dynamic reflections (7 total) it would be more efficient and as an added bonus would be more accurate. Although the downside would be giving up the environmental reflections so you wouldn't be able to see the environment on reflective surfaces like the car's body. Although how the game works currently is that the dynamic reflections only work with the player's vehicle (it would be extremely laggy if it worked for all vehicles and I demonstrate it below in action). So I propose to the devs that when you are inside of the vehicle, dynamic reflections will be turned off and the cameras use the "picture in picture" system like Euro Truck Simulator. This is because when you are inside of the vehicle, you cannot see the body of the car (well except for a sliver of the hood), so there is no point in having the dynamic reflections on. And when you are outside of the vehicle, it will use the dynamic reflections like currently for reflective materials. And so you would be able to display for example a back-up camera on the vehicle's infotainment screen without really sacrificing performance as it would only be visible inside the vehicle.
YES this would be so great... the real time reflections are actually distracting in some cars like the autobello where they show up on the inside of the a pillar which is quite unrealistic... with some mods its especially bad as the inside of the windshield is reflective and reflects the street which lokks wonky as fuck.
What would also be cool is dynamic dynamic reflections. Only have it on for parts the player can currently see.