I would like to cite somthing that crossed my mind,
It would very well be minato was a Sage like naruto too ! .. and the reason he simply did not use sage mode is because he did not have time to collect sage chakra during kyuubi fight..
And one morething!
It could very well be Minato saw the future with the help of sage frog telling him about the attack during narutos birth and consequences etc, about his future and narutos future ..,