Rankyaku is something Sanji should have easily be able to learn, but i guess he would be too similiar to Zoro. Considering his leg strength, he would cut everything to pieces. I don't think we will get it.
I do hope for some Range AOE type of attacks. I mean Sanji technicaly has alot of range, if we look at his Hell Memories it burns gigantic targets, but he never uses his fire to engulf everything in fire. So he got AOE with fire, which he never uses..., but no range attack, even tho what is holding him back from kicking fire balls or like a Fire Fist type of attack.
Don't know what Oda is thinking...
But i hope he gets atleast some sort of blunt range attacks - something like Garp has. Like creating insane shockwaves with his kicks that work like an Air Canon basicaly.