[Blind Spot Warning] would be a good safety upgrade for [Fit Wing Mirrors]
you mean like the little sticker things? or the mini-window you sometimes get added on?
I do plan soon to add folding wing mirrors as an option, which is cool because it could require servos to make them 
plus heated wing mirrors…requiring heaters
This, Looks like it would be door, or trunk, I would vote trunk, as the doors have a lot going on now.
Depends on the system being used I think. Looks like Nissan uses the rear camera for it and the indicator is on the inside of the car. Audi uses sensors on the rear bumper of the car and the indicator is on the mirror housing.
Other companies (like Kia) put the indicator on the actual mirror themselves.
You would be correct though that the actual system that does the detection wouldn’t belong in Fit Wing. It might be a candidate for Fit Rear Bumper though if you went the sensor route.
Exactly This^
I admit I have never seen those before. We already have side impact collision system don’t we? (I’m currently on my laptop).