Killer will return with better blades and fight Beckman
I think Kid will be the one who will defeat Beckman. Oda is setting him up to have some role in elbaf, with Kid's ship sinking off the elbaf shore.
After what happened recently, Oda needs to give Kid at least one W in Elbaf and Beckman is the only person who Kid could realistically get a 1v1 against.
Shanks is just out of his league. His story is too important to Luffy and Teach's for him to fall to Kid. Kid could rematch against Shanks and not get one shot, but he would still lose. Anyone weaker than YC1 is too weak. Shanks already ranked Kid above Lucky Roo. If Kid fought someone YC2 level in Elbaf, it would just dehype him and make him look like a massive fraud.
Beckman is the perfect matchup for him. He is a gun user, just like Kid(damned punk is his new signature move). He took Kid's arm. And he is hyped to be one of the strongest right hand men. Defeating Beck would allow Kid to redeem himself after his massive loss to Shanks, while also not giving him too much of a focus in an arc that will primarily be about Luffy, Teach, Shanks, and Cross Guild.