We shall is never grammatical acceptable. It was not correct back when people heated their water in a kettle;š§ it is not correct now in the age uncouth Colonials heat water in the microwave oven.šWhile "We will rock you" sounds great and confident, "We shall rock you" sounds "weak" like we want to rock you but we might not be able to.
The late Queen, Freddie, would roll in his grave if anyone sings, "We shall rock you."š®āšØ