Prediction time, maybe the kamabakka cake posseses genger-bending powers that will turn Big Mom into Big Daddy.
Thus making Luffy able to beat up Big Daddy, since the ultimate ability in One piece is being a woman, making her untouchable in battles(even unseen).
He will then proceed to defeat Big Daddy, making Luffy the ultimate Daddy (and pimp).
This sounds 100% plausible. I thought it would be a weight loss cake.