A neat feature from wipeout and F-Zero
Best way to describe it, is to provide a screenshot
An Indicator that tells you when an enemy comes up, where they are, an depending on indicator color how far they are away.
This way you can keep an eye on the track and prepare for some incoming stuff, lay mines or simply block of your enemy without the need of a Mirror or looking back.
I think it would be a nice alternative for systems that cant handle a Mirror for the lack of power.