I remember my story suggestion but it obviously doesn't need to be there is story of any kind could be very simple if they ever chose that decision. However they would need writers for the story and honestly now that I think about it , no need for a story really. Story could help but I think what keeps players far more immersed is the affixes and stuff.
Maybe something to motivate new players though is a very good thing but the game definitely gets easier everytime. Or something any kind of player would want to stay playing the game a bit longer since some things can get boring after a while.