...that would let you temporarily activate the backup/rearview camera. At least for a few seconds before it automatically switched back to your other view.

It seems there are times it would be nice, even helpful, to see what's going on immediately behind you while driving...things you couldn't possibly see in a mirror.

Does such functionality exist on any other vehicles?

 

You can add the functionality and more with a lockpick

 

Lockpick is just too expensive