It's going to be very hard to justify a potential fight between Luffy and Big Mom here. Through Law, we've seen just how much internal damage fucks her up (begged him twice to not use his Willie attacks).
So when you have Luffy learning both internal destruction and AdvCoC plus the fact he's immune to her thunder attacks it's going to be a one sided fight.
Having Big Mom be relevant outside the final war is not going to be easy.