Originally Posted by Human Rasengan
It would be extremely poor writing on kishis part to have a frog sage snake sage and no slug sage in what is known as the three way deadlock. Obviously Tsunade has a sage mode. She just hasnt used it yet. As a medical nin her main focus was always support not combat but based on her heritage kage rank and sanin title im sure she has sage mode as well
I think that Tsunades creation rebirth technique may be related to sage mode. Considering that Sakura has low chakra reserves she would have to store chakra until she has sufficient amount of chakra to use sage mode. I just realised how easy it is for Sasuke to learn Sage mode as well. Since Sasuke has used cursed seals which came from Juugo he should already know the feel of natural energy. This with Juugos flesh he received after KB almost killed him should allow him to use Sage mode.