Pluton is the power the take life. Poseidon is the power to control life. Uranus is the power to give life. What does controlling storms have to do with giving life? The storms is most likely Dragon's DF ability.
The top piece of Uranus contains the power to give life. The Gorosei has the lower half of Uranus(The staff held by the Gorosei with a black hat) that can only extend life. The Gorosei wants the upper half of Uranus and that One Piece of it is located in Raftel.
Remember Enel's cover story when he was looking at ancient drawings? The 3 people in the painting respresented the ancient weapons. The guy with the fishhead respresents poseidon, the guy with the battle gear represents pluton and the guy with the Skypia-like clothes represents Uranus. He was holding a staff that had a big stone or gem-like thing at the top of it. The gem at the top of it is One Piece.
The Ancient Weapons were said to be
weapons of mass destruction. Now, it would make no sense for The Gorosei to be able to extend life and/or Dragon having a DF that allows him to control weather.
Think about it. Look at the many DF's we have in One Piece, none of them allows the user to control something that they didn't generate themself. That would be too overpowered and is unheard of. Dragon was somehow able to control the sky itself. Wherever he went there was a storm and he was able to create a huge gust of wind without even moving a finger. That is beyond overpowered. Oda wont allow something like that as a Devil Fruit. Lets be realistic here. Dragon would solo the verse.
Even with others, have you seen Aokiji control ice that he didnt generate himself? Have you seen Ace control fire that he didn't generate himself? No. You eat a DF and it gives
you power. The devil in the fruits goes inside your body. Now how is a Devil going to go inside your body and somehow give you the ability to control sky itself? Overpowered, unrealistic and simply unnecessary considering that we have Uranus already to fit that task.
Poseidon: God of the sea
Uranus: Personification of sky/heaven
The Ancient Weapons are said to be weapons of mass destruction that will allow someone to either rule or destroy the world with it.
Also, on the whole "Uranus gem" thing. Its not really plausible as the rest of the figures also have plenty of things on them that have nothing to do with the ancient weapons. But you can see that Uranus (not sure if the guy with a "gem" on his staff is supposed to be Uranus") but if it is then you'll notice that he has a staff.
What is Uranus associated with? Personification of sky/heavens. Control over storm, clouds etc.
Now a STAFF that controls storms, clouds etc. would be Nami's clima tact. Uranus is most likely not Nami's clima tact but taking into account that it has something to do with sky/heavens i think thats a good hint on what Uranus could actually be just on a larger scale.
The fact that Dragon can control the sky itself already confirms that he has something to do with Uranus. Whether he has it or he is it i don't know but what he pulled off in Loguetown and the storms he keeps creating are similar to Nami's clima tact abilities just on a way bigger scale.
Now, that theory about the Gorosei's staff being able to extend life is very unlikely. Bonney already has a DF that allows her to give herself and others youth and Akainu already captured her yet 2 years later we see her eating and roaming free out of ID. If life extension is indeed necessary the marines would've just used her therefore Uranus being able to extend life is a waste of space because we already have a DF for that.
Anyways, the Gorosei's staff being Uranus is a very far fetched theory (although i kinda like the idea of giving eternal life). Dragon has already proven that he is able to control the sky itself and lets be honest here...you and i both know that no Devil Fruit in existence can allow an indivual to control the sky itself. Not to mention he did it without lifting a finger.
If Dragon with only a DF can pull that loguetown feat off without lifting a finger then a pissed off Dragon would solo this verse. Not happening.
I like the way you're theory but i honestly don't see One Piece being a gem.