In chapter 907 we see Shanks is at Mary Geoise and he speaks to the Five Elders in person to talk about “a certain pirate”.
From that moment many have wondered: is Shanks a good guy or a traitor?
In my own opinion, Shanks is a SAVIOR
-Shanks intervened at the right moment to save Luffy from the king of sea (When he lost his arm)
-Shanks intervened at the right moment to warn Whitebeard about Blackbeard
-Shanks intervened at the right moment to stop the war of Marineford and save Koby from Akainu and all Whitebeard Pirates (In the same time Luffy).
-Shanks intervening too at the right moment to warn Gorosei about something important too!
I think that Shanks can predict the future or more, he literally can see what will happen in the future! It’s for this reason that the World Government is scared of him, and as honest known pirate, they know that they have nothing bad coming from Shanks, and even if they want to act against him, he will win since he know the future and how all this will end!
-Sengoku accepted to stop the war because Shanks decided that!
-The Five Elders accepted to exchange some words with him because he is Shanks!
We all know too that Shanks’ power is based on a strong Haki, his Conqueror’s Haki even cracked the ship of Whitebeard!!!
So, my conclusion is that Shanks holds a strong Observation Haki that let him to see very far in the future! So he intervened here to give some help to Luffy & Straw Hats by warning the World Government about a fearsome enemy that will get in their road!! Perhaps the Legend teased by Oda.
*Theory by bcashier