I think that it is just a
I think that it is just a design choice, and that Tesla was working to design a very clean, simple interior design. But with that said I have grown to rely on the side mirror blind spot warnings, and heads up display warnings, and seat buzzer in my Cadillac ELR. The nice part as you mention is that you are normally looking at the side mirrors when changing lanes, so having the warning there makes the most sense. If there is a car in my blind spots then the mirrors light up yellow, and if I signal to change lanes and there is a car there then the yellow lights on the mirror flash and the driver's seat buzzes to warn me. And if someone stops suddenly in front of me and I am not already stepping on the brakes, then bright red HUD lights shine on my windshield, and the seat buzzes. Another feature that I have seen in some other cars is an aerial view which shows 360 degrees from above with your car in the center.