As many zoro fans have stated in the past, there is a multitude of build up and foreshadowing for Zoro vs Kaido. This doesn't mean zoro will beat kaido, however given that kaido will obviously be a tag team fight, it is clear that Zoro will play a crucial role in kaido's defeat. In fact, when Luffy and Zoro were in the plaza with Queen, apoo, and the headliners, zoro specifically stated that he didn't want to take damage because he wanted to face kaido.
If zoro just wanted any strong fight, he could have taken on Queen or apoo. He didn't, because he has his mind set on kaido.
Sanji and Jinbe, due to their actions on WCI, have a lot of set up against big mom. One of big mom's only weaknesses is her hunger and out of all the people in the alliance, sanji is the only one who can exploit this weakness. I think it is inevitable that Sanji will bake another cake. Somehow, the alliance can then use this cake to take out big mom. For example, they could attack big mom while she is eating, or destroy the cake immediately after showing it to big mom, sending her into a rampage, ect.
In any case, with Luffy and others fighting kaido, the only way to bring down big mom is with a cake.
@ShishioIsBack I'm sure you don't think Sanji is so incapable that he can't help bring down big mom in this way.