As said above, I don't think Naruto used the Thunder God technique. I think he just had such massive speed that it looked like it.

That being said I think it's highly probably that Naruto will learn it, and with his massive chakra and speed will perfect it beyond Minato.

We have still yet to see "that jutsu" or w.e aren't we? (I actually don't remember if we did or not...)... Anyway, as I said, I am guessing Naruto will learn a technique that combines both his/fox's massive speed and chakra with the Thunder God technique.

As for Sage mode, I don't think it's really redundant. It prepared Naruto to take on Pain, and also helped him survive until he gained control over the fox's power. I also think that the focus and training it took for sage mode will help Naruto handle the fox's power.

Besides Naruto is a stamina monster now, even more then before, and who knows, with all the sharingan hax that Sasuke gets why shouldn't Naruto get a super-demon-fox-sage-mode (beyond the one we seen with Nagato now that he controls the fox)?