I’ve actually thought about this a lot before I came across this thread. In my mind it can only be Luffy. Specifically, Luffy as the Pirate King. What better way to show him become the ultimate pirate than for him to don the most stereotypical and powerful piece of pirate imagery? As for how he would lose his eye, it would have to be right before he found One Piece so it’d be in his supposed battle with Blackbeard at Raftel. No doubt from the same attack that scarred Shanks so long ago.
To go even further, there’s an allusion to make with all of this. Oda loves Vikings and is probably familiar with the Norse myth of how Odin gave up an eye to drink from the well of wisdom. Well, what sort of hidden wisdom or knowledge exists in the world of One Piece? The poneglyphs. In discovering the Rio Ponelgyph on Raftel, Luffy will lose an eye. It won’t be anything too literary and deep but One Piece is full of quick, little nods and references like that to stories and culture.
Now for my really absurd theory: One Piece itself is an eye patch.