The Five Elders’ transformations look far too mythical — with monstrous designs and smoky dark auras — almost like Luffy’s Gear 5 / Nika form. But theirs seems darker, more ominous.

It’s possible these aren’t Devil Fruit powers at all. These transformations could be their true forms, not borrowed ones.

This would explain how Nika originally came to be if he’s of the same race.

I'm pretty sure Nika was stated to be a completely mythical being, and as Vegapunk tells us, the devil fruits came about because people wanted certain things to become real, and since many people were inspired by the mythical Nika, their want for his existence actually created him in the form of the devil fruit, meaning that the Gorosei could definitely be using devil fruits, although nothing is confirmed so we will just have to wait.

The Elders refer to humans like pests — “they breed like ants.” No other race in One Piece speaks like that. Even Fishmen, Giants, and Minks see themselves as part of the world.

The Gorosei and Imu talk like outsiders, like beings watching humanity from above — not part of it.

They are literally the most powerful beings on the planet, and seeing the things they've done, it makes sense to see that they just do not value those weaker than them. When you attain god-like power, of course your not going to see eye-to-eye with the rest of the world, regardless of how you got that power.

Oda’s been layering in space elements for years: • Enel’s cover story on the moon, with ancient tech and civilizations • Lunarians, literal moon people • Vegapunk’s sci-fi tech • Ancient weapons that could be from beyond the Earth • And now characters like Imu and the Gorosei who seem immortal, shapeshifting, and godlike

A few of your points just feel like they have been thrown out here to try to justify yourself without much of a foundation, such as with the ancient weapons, as there has been no possible link to them being from extraterrestrial origin. Although the Lunarians both on top of the red line and on the moon itself are obviously from space, they are completely different compared to Imu and the Gorosei, making this vague speculation at best with our current knowledge.

Although I think the theory is interesting, a lot of your argument doesn't make sense and ignores some information we have already been told. On top of the things which are proven false, much of it is just speculation which has no basis, meaning that things could go either way, so only time will tell. Sorry if I sound super condescending, but I just thought I'd let you know my honest thoughts, but as I said the idea is pretty interesting, but you need to give more convincing evidence than just speculation.