Now that the Shepherd family's weapon is revealed to be a sword, I think Ju Peter can be removed as a future Sanji opponent.
Oda will likely have Sanji fight non-sword God weapons like the spear, and in the future could be Axe, Brass Knuckles, Boots, or whatever.
Nope, who says Ju Peter can be removed? Just because the sword Gram is already being used that doesn't mean Peter can't fight Sanji, there is no rule that says that.
Peter might not even use a weapon if he fights against Sanji.
And in a case for Zoro vs Nusjuro, the sword Muramasa might belong to Nusjuro's family, but Nusjuro might not use it, and will instead just use the Shodai Kitetsu.
You are on the assumption that the Elders will have to use the weapons as well, but the thing is they might not use it.
So no Peter is not ruled out.
He was never supposed to be Sanji’s opponent, Mars is.
Naw it will be Peter not Mars(Not against Mars though), I don't think you get what Oda is trying to do.
Zoro and Sanji's fights in this current arc is against Sommers and Killingham, Zoro is fighting a Sommers who is a member of the Shepherd Family, and Sanji is fighting Killingham who is a mythical centaur.
Now look at the Five Elders, Ju Peter is a member of the Shepherd Family and Nusjuro is a mythical centaur.
The whole point of Oda having Zoro vs Sommers and Sanji vs Killingham, is so that way when they fight against the Elders, the matchup will then be switched.
There is also a reason why when it came to the Five Elders(With Saturn) both Peter and Nusjuro stood out in terms of design compared to the others.
Sanji imo was always going to fight at least one of the Shepherd Family members, and the whole Sanji vs Mars always depended on his Elbaf matchup.