That's possible, but didn't Madam… (What was her name again?)... Well, something, predicted that Luffy would be the cause for FI destruction? I don't see the mer-people becoming his friends then... Unless he's not the direct cause, which we are still to see.
Anyway I don't see Luffy protecting FI, directly or indirectly. That is now Big Mom's territory. Comparing one to another, no one would care about Luffy's name next to Big Mom's. Correct me if I'm wrong in anything, please.
To Monkey King, where's your respect for a senior? It's true that it's not how long you've been on a forum that makes you better, but don't you think you're crossing the line?
Really after the war luffy has to be one of the most notorious pirates around. And what ever the prophecy holds it will only lead to more enemies latter on. Big mom won't sit by and watch some rookie ruin the island she has taken under her wing, it would be insulting to a younkous name.