Here is what I think, Jiraya show him a theory he came up with to use the rasengan as a shiruken, so when he was show shape manipulation he realize it could be done, but he couldn't do it since the 9tail chackra would take over him, so after he mastèred sage mode he realize that "it" could be Done
Bytheway it would just be called the complete RasenShiruken
Good Theory! It certainly makes sense. Let's see what Kishi does with it now.
On another note,too bad the nnietails chakra is too strong (and evil) for Naruto to control, because Sage mode has its annoying downside.