Alright hear me out, I think I just completed my 
The Straw Hat is a Parasite theory:
The immortality surgery is the explanation for why Imu and the Gorosei/Holy Knights are immortal. The Ope Ope no Mi is not the only method to make people immortal.
Saint Shanks actually received the immortality surgery and can heal, however he received one wound in his life that he could not heal from: the scar that Blackbeard gave him. This is why Saint Shanks is so spooked by Blackbeard and why he wanted to discuss Teach with the Gorosei, because Saint Shanks doesn’t understand why he can’t heal from the wound Teach gave him.
This also explains why Imu feared Joy Boy and Davy Jones: because immortals cannot heal from their attacks
Saint Shanks can actually heal his left arm, but he is choosing not to in order to continue his masquerade upon Luffy. The Straw Hat is a parasite that is stealing some kind of dormant power from Luffy, probably the dormant power that prevents immortals from healing (this is how Luffy will defeat Imu).
And so this is how Elbaph will connect Luffy and Saint Shanks: Luffy and Imu will fight, and Imu will realize that Luffy has a power that prevents Imu from healing. This is when Saint Shanks shows up and banishes Imu with Joy Boy CoC that he gained from Roger (the Straw Hat), and just when Luffy thinks he and Saint Shanks are about to have gay sex: boom. Saint Shanks regenerates his left arm, steals the Straw Hat from Luffy, and with it Saint Shanks gains the power he has been slowly stealing from Luffy ever since he gave him the Straw Hat: the power to kill Imu and usurp the throne for himself.
I figured it out my guys, this is the arc of Elbaph.
@Blackbeard @Bakura @ZenZu @comrade @Sentinel @Tyki_Mikk @MarineHQ @EmperorKinyagi