Personally I think he already ate his 3rd devil fruit a long time ago and that will be the biggest reveal in his backstory.
I do like to clown Shanks but I'm not convinced Teach did a number on him without a fruit. He's so traumatized that even as a yonko he went through all the trouble to meet Whitebeard, reiterating how he wasn't offguard. This means Shanks was strong enough back then and not even Mihawk could cause a scar this significant.
No one but Shanks recognized his strength, maybe he was the only one to see his true form. He does mention to Whitebeard how he has been hiding his strength and it can't only be CoA and physical strength, and we know he's not very skilled lol
This is what Ace tells Shanks about his scar
There's a reason why he can eat more than 1 devil fruit, has a weird body, "they" etc, he's a D. so it can't be a new race.
In Ace's novel he literally eats flower bouquets lol