Several points that make me think that Shanks is the Yonkou who owns Elbaf’s island.
In this theory, I will claim the points that make me think that the protector of the island of Elbaf is currently the Yonko Shanks.
I – New World Territories Functioning
Elbaf is the island of the Giants species in the New World.
The islands of the NW we saw till now are :
– Fishmen Island, under the protection of Big Mom (previously White Beard).
– Punk Hazard, under the protection of Caesar Clown, linked with 2 Yonkos and with Doflamingo (previously it was owned by the WG).
– Dressrosa, under the protection of Doflamingo, now under Luffy’s.
– Zou, independant island but led by Nekomamushi and Inuarashi, former pirates of WB and Roger.
– Totto Land, under the protection of Big Mom.
– Wano, controlled by Kaido who took it by force.
In the New World, most of the territories are owned by the Yonkos.
Elbaf is foreshadowed since a long time, and the Straw Hats will go there for sure.
But it’s hard to tell how this island works, who owns it. I believe the most evident Yonkou candidate for this is Shanks.
II – Viking’s Thematic
So, basically it’s pretty obvious that the Giants of One Piece are inspired by the Norse barbaric explorers : the Vikings and their mythology.
Gungnir is the spear of the god Odin, chief of the Norse Pantheon.
The epithet of Shanks is “Red Haired Shanks”.
First, his inspiration comes from “Calico” Rackam Jack, famous pirate which the flag inspired Shanks flag for the Red-Haired Pirates.
But also, Shanks is isnpired after Erik the Red, a Norwegian Viking.
The “classic” ship of the Viking is called a Drekar. The bow with a shape of dragon.
It’s basically what Shanks possess : the Red Force.
Also, look at the ship and the flag of the original Giants Pirates crew :
Lastly about this, I’ve found from some french theory I will link at the end this connection :
Shanks is also inspired after the god Týr, associated with law and heroïc glory in Norse Mythology.
Tyr is a one-arm character who sacrificied his arm to the monstruous Wolf Fenrir.
Remember the Sea King and Shanks sacrifice ?
III – Similar view with the Giants
Shanks showed since the very beginning the “spirit” of One Piece, about freedom, adventure, pirate’s life and honor values.
Shanks is someone who respects what he says and had honor values. He’s brave and respectful. He likes to fight, act, travel, make parties and enjoy time.
He is a proper “good” pirate.
Something what the giants do share.
Sometimes, the Elbaf’s giants were depicted as “barbaric” but this was the point of view of Jaguar D. Saul, from the Navy who understood the real barbary because of the World Government decision.
But, from Usopp perspective and Elbaf’s giants themselves, they look like good people.
Shanks is a man who trusts in dreams, avdentures and will. He’s the symbol of the conquest and the wish.
IMO, the Giants from Elbaf share the same feeling about life.
IV – Usopp and Yasopp’s connection to the Giants.
Yasopp is one of the top fighters of Shanks, he’s a trusted man in the Shank’s crew and took the choice in his life to go to adventure and flee from his life with his wife and his son.
I believe the Usopp’s fascination for the Giants and the aventure’s desire comes from his father.
I believe Usopp will meet his father in “his” arc : Elbaf’s arc.
As Sanji is meeting his Father Jajji in the WCI arc which his the “Sanji’s arc”. I think it will be the same for our sniper.
V – Foreshadowings or entries for “Shanks during Elbaf”
Look again at the Shanks’s flag and scar.
It clearly looks like the original symbols and flags of pirates in pop-culture and history.
Does this one-eye thing about Hajrudin at the end of Dressrosa could be a foreshadowing that Shanks will have a big role during Elbaf’s arc ?
Also, in chapter 802, we saw Buggy the Clown, who becames Shichibukai and owns the “Pirate Dispatch”.
He had under his “wings” the crew of the New Giants Pirates led by Hajrudin.
Buggy and Shanks have a lot of history in common, they are kind of “good” friends.
What if they will be present together during Elbaf’s arc since Buggy has ties with the Giants …?
VI – 4 Yonko Saga Order
We are currently in the “4 Yonko Saga” since the WCI arc started.
That means it’s really likely to have an arc for each Yonko.
We are right now with Big Mom.
Next one is obviously Kaido in Wano.
This leaves Blackbeard and Shanks, and Blackbeard will be the last pirate boss for Luffy, after Blackbeard probably kills Shanks.
And we know, Elbaf will appear for sure. So, Shanks crew in Elbaf could be the best shot! Quite logical and likely.
*Theory by Zero Zero No Mi