We'll just have to wait 'n see. I don't know why Oda has hidden his face yet not his body, the only reason in my mind that comes up is a badass reveal of his face with an eye-patch. Also, Sabo was a kid when he got hit with that cannonball, him getting injected with hormones at such a young age, doesn't sit right with me. If anything, I hope he was given anesthesia and then being operated on.
This discussion won't even matter, he'll be revealed pretty soon and this is all speculation (albeit fun). If he doesn't have the eye-patch, then oh well lol It'll be sweet when we actually get to see a character with one in the manga.
I think his face isn't revealed because oda wants to give him the proper introduction. I wouldn't be surprised if he didn't have any facial scars what so ever.