May as well post these combined thoughts here. Seemed a bit TL;DR for the Theories that don't deserve their own thread and didn't quite seem to fit in anywhere else.
Monkey D. Dragon & the Ancient Weapon, Uranus
We have two that are confirmed:
PLUTON: A battleship that was so powerful it could one-shot an island.
POSEIDON: A mermaid with the ability to control Sea Kings.
As per literature we have them also happen to match their corresponding mythical theme:
Pluton – God of the underworld (Death)
Poseidon – God of the Sea
Uranus – God of the Sky
It was also mentioned in the “Pluton, Poseidon, and Uranus” thread that Uranus, in greek mythology, was associated with the energy of revolution; not in a chaotic or disorder sense, but a new level of understanding or a new way of thinking. Well, Dragon happens to be the revolutionary leader set out to unite countries under his banner, so likely Uranus and the revolutionaries will have a very close connection.
Smoker & Tashigi, and Moral Justice
In the OP world, what is truly justice? Doflamingo outlines this perfectly for us. As he states; history is written by the victors and true justice in this world is best left to one's own interpretation, a theme concerning the idea of the word that constantly reoccurs throughout the series. Regarding these two characters:
Both have their own sense of 'justice', a contrast to the 'Absolute Justice' regime from Sakazuki. But who, truly, has been shown to have a truly honorable, moral way of justice? From the manga's POV, it is inferred that the Straw Hat Pirates have the 'best' or most 'appropriate' sense of the term 'justice' – more often than not clashing with other interpretations.
Their relationship with these three characters is especially important. Despite being on opposite factions and the whole Smoker trying to kill him thing, Luffy somehow likes him and Tashigi. This leads to my prediction:
Smoker & Tashigi will join the revolutionaries later on in the New World (if they don't join the Straw Hats)
Twice now (was it more?)in Arabasta and now in Punk Hazard – both the first major long arcs pre and post timeskip respectively, their ideals and those of the SH have somehow met in the middle, the relationship almost parallel in nature sometimes;
-Smoker ends up in a cell with some of the Straw Hats.
-Luffy saves Smoker through Zoro.
Smoker sits back and lets Tashigi decide for herself, which leads to:
-Tashigi berating her command and called it disgraceful for suggesting that they take out the Straw Hats after the battle when they were all defenseles.
-Smoker ends up in a cell with some of the Straw Hats.
-Zoro saves Tashigi from Monet (and carries her over his shoulder.)
-Smoker teams up with Law and Luffy vs Vergo and CC.
-Tashigi berating her command and called it disgraceful for trying to portray the SH as evil, then amused when they revealed they were just afraid of admiring pirates.
Robin even demurely pointed the first one out while they were all locked up by CC.
Former Admiral Aokiji
Well, similar to Smoker and Tashigi, Kuzan's only real transgression has been against the Straw Hats and bad guys, and was going only after Robin in their first encounter. He's shown to have a benevolent nature later with decision making, some of which are significant to his character development.
The Ohara Incident
! Aokiji, a VA at the time, was leading CP9 to apprehend the scholars for forbidden research on Ohara. The original orders was to deal with the scholars only and let those not involved escape freely. However, VA Sakazuki ordered instead to burn the civilian ships as well, which completely went against Kuzan and foreshadowed the future clash of their ideals regarding what defines 'justice'.
! Kuzan was still very loyal to the marines at the time, even regretfully killing his friend in Jaguar D Saul for being involved with the archaelogists. However, his dying friend argued to him whether this was a moral thing to do or not, marking the beginning of Kuzan's internal conflict about the marines and Justice.
! Kuzan gave Robin a small boat and a means of escape with the stern warning not to cause trouble, or he would go after her – which she ended up doing anyway in life.
Sparing Luffy prior to Water 7:
! When he had the option to kill Luffy after their 1v1, he spared Luffy, saying that was his favor for defeating Crocodile in Arabasta – despite Smoker's superiors twisting his story in his favor. This implies that Smoker and Kuzan have been friends (or at least close acquaintences) as far back as Arabasta. Because Smoker's already somewhat rebellious towards his superiors at the time being, I'm going to lean more towards friends.
! Kuzan also implied that Crocodile had in addition to his account of the events, said something else 'stupid'.
! Since he's standing in front of Luffy and considering his use of the word “stupid”, it heavily implies that Smoker's mystery comment is regarding only Luffy. What could it have been?
! My bet is that Smoker said something regarding the comparison of Luffy to Roger.
! Smoker is one of the earliest marines to recognize the true threat of Luffy. And not just as a D; something much grander: The Pirate King.
! This little wildcard deduction was made by Smoker while witnessing Luffy on Roger's execution platform. How? Because he was standing there 22 years ago when Roger was on that same platform and saw the exact same smile on Luffy's face. And when he made his account to Kuzan, he added the bit with Luffy/Gol D Roger. Kuzan, not having witnessed what the Straw Hats were capable of then, must have dismissed the idea as 'stupid'.