Agreed, though it would be cool if in a KH movie they could slip some plot between the constant fight scenes, unlike AC. I wish KH3 was the last one too.
But yeah, like people have said, Sora will remain the series' main character, though there is almost guaranteed to be another keyblader or two jumping in as minor characters. I hope Nomura actually plans on developing Sora's personality at some point, otherwise he's gonna get boring fast.