I just want to point out few things:
1. Zoro Scene in Punk Hazard where he got angry & told Luffy to get serious
2. Zoro Scene against Queen where he got angry & said that he isn't there to play Games
3. Fishmen Island Scene when Zoro told Luffy that if he doesn't have CoC then he should step out as Captain
4. Zoro's Scarifice against Kuma that only Sanji & Robin know of
5. Zoro's Reaction to Sanji leaving the Crew & what he told Luffy
+ Other Statement about Zoro taking over here & there
Is Oda building up towards Zoro leaving the Crew??
Many Straw Hats left the Crew after they joined (Nami, Usopp, Robin, Sanji & even Jinbe joined late)
So this is clearly an Idea that Oda likes to repeat & if it's because he is preparing one for Final Arc then it should be about Zoro
If Luffy doesn't beat Kaido or Big Mom & Zoro finds himself performing a little better. Then Oda might indeed take that route & make Zoro leave the Crew