If Elbaf becomes a Shanks arc, Shanks isn't going to be defeated by BB. BB is endgame for Luffy. And honestly, doesnt seem like hes interested in going after Shanks. I don't see forsee Shanks making it to endgame. Now to my main point..
IF this is a Shanks-centric arc, He will be defeated by Kidd.
After reading this most recent chapter, we know Loki has interacted with Shanks in the past and hes clearly not fond of him. And we also can tell how Luffy still views Shanks...And obviously we know how Kidd views Shanks...
Luffy admires Shanks
Loki/Kidd dislike Shanks
The one who will free Loki, will be Kidd. Now this is where things can get interesting. Loki is a complete wildcard character. It's quite hard to tell what his next moves will be. So far, Oda has setup this arc masterfully. I'll list a few potential scenarios that could occur.
*The first thing to address is the key that will free Loki
Is there a potential the key that could free Loki could lead to conflict? Absolutely. I'm assuming wherever the key is held, its being heavily guarded.
I could see a scenario where Kidd attempts to retrieve the key and encounters whomever is guarding it. I could also see a scenario where Luffy is asked to help defend the key. In both scenarios, conflict would occur. Regarding the key, its a bit too early to say anything about it, but it could definitely cause a fight.
Now regarding what would happen when Loki is freed:
Kidd/Loki vs Shanks Luffy -> Loki trains/teams up with Kidd and they fight vs Shanks/Luffy
Kidd vs Loki - Loki gets freed and comes into conflict with Kidd. Loki strikes me a conqueror. If they have a reason to fight, they will.
Luffy vs Loki - A possibility.
Kidd/Loki vs Elbaf (Luffy + giants) -> Kinda similiar to the first one listed
Kidd vs Luffy -> Shanks(and i guess Loki), will be the catalycst for this fight. Everyone laughed when I said the way Kidd and Luffy view Shanks will cause a fight. This most recent chapter is perfect example. Loki barely joked around about Shanks, and Luffy was ready to slam him with G4. As I've said countless times if Kidd/Luffy ever reveal to each other, the way they view Shanks, a fight will happen 100%.
The two scenarios that I believe are most likely:
Kidd vs Luffy
Kidd/Loki vs Shanks/Luffy
*Something else to note. It's possible "Thor" could play a role if he exists. Something interesting I noticed, wad that, on the Damned Punk kidd was using to destroy Shank's fleet, the word "Tor" was written on it. Could this be referring to something?
And honestly, there are ton of wildcards potentially for this arc.....Loki, Shiki, Other giants, the realms, Shanks, the burned man, the silhouette man, etc...