I don't think Sage Mode works like that. Kurama is not a physical entity when he is inside Naruto. He can recover his own chakra, but I don't think he can absorb Sage Mode without an actual body. However, now that Kurama and Naruto are on good terms, Naruto should be able to merge with the toads in order for them to gather nature chakra for him.
I agree that it would be pretty awesome to see a Sage Mode/Kyuubi Mode combination. Kishi has hinted at it a couple of times already, but Naruto is overpowered as it is. Over the past few days in the manga, Naruto has "tamed" Kurama, fought on every battlefield, battle with two current Kage, fought with the other Jinchuriki, and battled Obito. After all that, he was still able to defend the Shinobi Alliance against some of the Juubi's attacks and is still going strong. Imagine the current battle, if Naruto was anywhere near full strength. In other words, Kishi has to give some other key characters (i.e. Sasuke and Sakura) some significant boosts in order to even catch up. Plus, Naruto is probably already going to get another power up from his connection with the Bijuu.
