Okay, I had a random idea that won't leave me alone, so now you all have to suffer along with me as I relate this incredibly unlikely idea.
But, what if Loki's Fruit is actually the "Superman" Fruit?
Superman is powered by the sun, thusly counting as a "Sun God" of a sort.
Loki's eye's are covered by bandages, hinting that this power has something to do with eyes or potentially eye-beams. Superman famously has eye-beams.
Loki is tied up with chains. Superman is famous for images of him breaking chains that bind him.
Loki is surrounded by wolves in the forest. Superman has his super-dog Krypto.
Loki is imprisoned in a wintery area of Elbaph. Superman has his Fortress of Solitude in Antarctica.
Plus, there's the whole "Nika the Comic Book Character" theory.
Now, personally, I don't subscribe to the theory, myself. But, let's just say for argument's sake that Nika will turn out to be a fictional comic book character come to life via the power of the Devil Fruits. If that were to be the case, then Oda would probably want to foreshadow that in some way. Having Loki turn out to have the Fruit from another comic book-like character would work as foreshadowing the Nika reveal in the future. And there's very few characters who would scream "comic book" more than the world's very first superhero, Superman.
It all works better than it should. (Even if a lot of these "connections" are incredibly tenuous, at best.)
Now, this couldn't actually be "Superman", since he's a copywrited character owned by another corporation. But, there are PLENTY of Superman parodies and rip-offs around. I could totally see Oda creating another Superman expy for the manga. A "original character" who is close enough that everyone KNOWS what he's referencing, even if he can't say it out loud. In fact, one of Oda's major inspirations Akira Toriyama did the exact same thing with "Sourman" and "Bibibinman" from Dr Slump and Dragon Ball.
Now, this is probably not going to happen. I don't even think I WANT it to happen. But, it's such a weird random idea, that I just had to write it down.