It's certain that Naruto's sage mode is longer now without fusion. Remember, I think this is correct, that Naruto was dividing his chakra four ways because the Kyuubi chakra, now that Naruto has it sealed away and only used at will, he should be able to split his chakra only three ways. This is approximately a 33% increase. Now if he has two shadow clones like against Nagato, it adds to about a 100% increase! Thus, without fusion he doubles his nature chakra, so instead of a 6 FRS limit, it's now 12.
However, I believe this is an underestimation because he was working on prolonging his time in sage mode just prior to his most recent encounter with Team 7 around the Kage summit.
Now, I don't think that Naruto will ever fuse with Ma and Pa toad because this was Jiraiya's signature/ultimate mode, and Naruto needs to be different. Thats's a literary reason. Personally, I think he'll fuse sage and Rikudou mode somehow; that's kind of his way of doing things. He solves problems in novel ways, so he probably use a method people on the forums have speculated on.