Shady Shanks.
Mine is a personal theory, the option of someone else taking Kidd's arm is still dominant, and in that case I expect Shanks to be the material executioner.
Fact is that I think Shanks can move smoothly in that
gray enviroment without necessarily covering his Gryphon of blood but rather by forcing his opponents with his internal willpower (aka extreme Conqueror nature) or, as an alternative, blackmailing/playing death games.
Kidd could rapresent someone who, as a Rookie, was impressive enough to make Shanks leave (as a winner) without more casualties. Shining for his indomable nature.
Wouldn't be surprised if, while reading the news, he comments about Luffy AND Kidd, dropping a subtle reference about the last meeting..
Then chill and let this place burn down