It's gonna be up to Malzahn and Lashlee make Marshall an top-flight SEC-level passser... all in about a three month period.
I wouldn't even say he has to be developed into a top-flight SEC-level passer.
If he can break down defenses with his athleticism like we hope he can (a la Cam, but smaller, but FASTER), then the passing game will open up for him. In other words, I don't think he's gonna have to thread the needle very much (i.e. top-flight), just hit the open man (adequate-to-good).