Really ?
People have been speculating when Naruto would merge modes for months now.
I can hardly believe that you have been on this site and not run into that discussion.
Secondly it is not a actual power up per'say,Kurama is allowing his chakra to mix into sage mode so when naruto does enter the form he can gather sage energy at a faster pace and in larger amounts.
I mean if you did not believe it back then,then surely you should of had at least guessed that naruto would try to use sage mode considering only senjustu works against juubito.