One thing that really irks me off about the Zoro & Sanji fanbase is the sheer favoritism & utter lack of objectiveness from a large majority of posters on both sides (particularly the Zoro fanbase - but I guess that isn’t really surprising given that it occupies a very large majority of the forum) and why I can’t really be arsed anymore participating in Zoro & Sanji related debates.
Rant aside, like I’ve already stated in the thread prior to this, I think both are more than qualified to have it.
1. Leadership Skills
Both have demonstrated good leadership skills at times when they’ve had to take the helm when Luffy couldn’t. Zoro has more of those with the crew, whereas Sanji has some with the crew & some outside of it (for example leading the marines on PH). Given the nature of Wano, Zoro prolly gets some feats with non-crew members as well. At the very least it’s been foreshadowed on Zou.
2. Both have demonstrated very strong wills, be it persevering for days on days through hunger or standing up to Kuma, willing to sacrifice themselves for their crew-mates even whilst battered & beaten.
3. Special bloodline
Sanji is Royalty & Zoro’s might have originated from the Shimotsuki clan, a clan that boasts the strongest Samurai on Wano & one which Ryuma is from.
Only thing tho, is that I feel it might be a tad too late for Oda to give it to either or both but we’d see. I’d personally prefer Oda to focus on their respective Haki specialities instead but again we shall see ^^