BigCrate if you are envision mirrors that you could see while looking forward there are 2 huge problems with them.
1. Think of the size that the mirror would be on your screen, Then envision how what you see now looking forward has to be compressed into that small area, and then how small the objects would be,or more precisly how most planes could not be seen.
2. To make a mirror is realy displaying 2 different views at once, hence you almost 1/2 frame rate.