Or at least, some numbers indicating when people are going to die. This came when I suddenly recalled the music video for the Nickelback song Savin’ Me (please don’t judge me!). If you watch the video, basically he has the (permanent) ability to see the remaining lifespan for everyone around him in the form of a countdown above everyone’s head. Can you imagine the implications of this ability, for a profession where death can be just a mission away?
Also, I think that’s a far more interesting ability to give Naruto than to have him get god-like powers and crush everyone with impunity. I’m not dissing Sharingan/Rinnegan stories because there are plenty of good ones, but some of them could do well to tone down Naruto’s strength a little.