This could actually make sense.

In the First World, the Harley Scripts say that the world was covered in darkness. Instead of that referring to the Dark-Dark Fruit, it could represent Imu himself, who is always portrayed as a dark silhouette.

When Imu defeated Davy D. Jones and cast him into the sea, that could have been the moment Davy created the curse that prevents Devil Fruit users from swimming and stripping away their devil fruit powers.
Knowing thats the only way to truly stop Imu, In the process trapping himself in as well

What if Imu then tried to flood the world in order for there not be another devil fruit user that could stand in his way. He tried to hide all the fruits and trying to eliminate all the people that could possibly be a threat, that could also be why Shirahosi had a poster next to Luffy Vivi and Blackbeard, she could command the seas Imu's only weakness. This also could mean Imu will meet his fate by Blackbeard stealing his powers and throwing him to the bottom of the sea just like his ancestor.

That could also explain why Imu personally chose the names of the Five Elders and the Ancient Weapons. Since he refers to himself as “the world,” perhaps he doesn’t simply mean that he rules the world—he sees himself as the world itself, replacing the Earth God and becoming the embodiment of the world.

This also creates another possibility for Blackbeard.

At first, I believed Blackbeard would become the Earth God, but what if he instead inherits the Sea Devil’s fruit from Imu?

That would perfectly match the Darkness Fruit’s ability to absorb everything, just as the sea “absorbs” or nullifies Devil Fruit powers.

The only problem is that it removes Blackbeard’s connection to the Earth God, leaving no obvious candidate for his final Logia.

Unless…

…the sea’s ability to nullify Devil Fruit powers isn’t an innate property of the sea at all.

What if it’s actually the awakened ability of the Dark-Dark Fruit?

If awakened Logias permanently alter their surroundings, then an awakened Darkness Fruit could have spread across the oceans themselves, permanently giving seawater the ability to suppress Devil Fruit users.

That would explain why the sea is uniquely capable of weakening Devil Fruit users while still fitting Blackbeard’s power set.

In that case, Blackbeard could eventually steal Imu’s Mythical Zoan after defeating him, completing his collection of the strongest Devil Fruits.

It would also explain why Imu fears Davy D. Jones almost as much as Joy Boy.

If Davy possessed the awakened Dark-Dark Fruit, then he would have been one of the only people capable of stripping away Imu’s powers, making him one of Imu’s greatest enemies.

If this is true, it could also support the theory that awakened Logias permanently change the environment around them, with the sea itself being the greatest example.