Naruto can use them both at once by using multi-shadow clones.

We've already seen this. It's possible that Naruto could combine them, but honestly sage mode add to 9 tails chakra mode or tailed beast mode. The fighting style is pretty different. Sage mode grants Naruto durability, strength, chakra, sensing, and frog kumite. He doesn't need any of these in 9 tails mode. He can feel other people's emotions, he has extreme speed, he can use the 9 tails cloak to fight instead of frog kumite, and he spams rasengan with chakra arms. Tailed beast mode for Naruto was like a susano'o in the shape of Kurama.
Naruto already find the most efficient go-between, using tailed beast mode and having a clone use sage mode. Different situations call for different modes.
