Temeraire/WMG

Dragons will be phased out of military use within Temeraire's natural lifetime
In the age of muzzle-loaded muskets it takes a very lucky head and/or wing shot to do worse than inflict a flesh wound on a combat-sized dragon. If tech development continues we are looking at gatling guns within 60 years, and once someone works out an internal combustion engine with a power-to-weight ratio sufficient to put on something airworthy we are looking at a human generation at most before we have machines faster and more readily 'fixed' than dragons carrying weapons that can kill them outright.
 * Armor tech may catch up to the point where dragons can take off with something that could stop contemporary weapons, but only several decades later.
 * Or, alternatively, draconic jetpacks.
 * Alternately, dragons realize that technology makes their one role in society obsolete and revolt.
 * Hopefully, by that point they will have citizenship and at least a few options open outside of the military (admittedly, without thumbs many occupations remain problematic)

Universal (Human) Suffrage will be accelerated by the draconic efforts at gaining citizenship rights
Call it a refinement of Black & White ganging up on Green if you will, but with oversized flying reptiles agitating for the vote quite a few un-propertied/catholics/what-have-you will ask "Why not me?" while many of the ruling class will consider it rather less outragious compared to doing so for 'beasts'.

The whole Longwing pilot thing will give the Feminist movement a leg up by simply existing.

 * Presuming they still keep the whole mess under wraps, those with clearance to know about... say...  will at least be somewhat more likely to keep thier mouths shut rather than parrot the common "wisdom" of female incapacity.
 * BTW, as of book six, this seems off the table.
 * If (as seems likely IMO) the truth of the matter comes out, then many a counterargument against Women's Rights get shot down. That being said the "suffragettes" are likey to split between those who hold the female aviators up as brave defenders of Britain and a true example for all women; and those who distance themselves from the 'mannish', 'licensious', 'unwomanly' creatures and thier beasts (if for no other reasons than the tactical).
 * The Martin Luther King, Jr.-vs-Malcom X Effect. They'll deal with the prim-and-proper sufraggettes because the alternative is dealing with Admiral Jane Roland, and her big, friendly dragon.
 * There may be active collaboration to that effect.

Dragons are mildly autistic
Only they're ALL the equivalent of autistic humans. They can have great intelligence, but they have behavioral and perception problems like an autistic kid. Or, of course, this is completely Unfortunate Implications misinterpretation of the way dragons are kept isolated and ignorant.
 * Doubt it, too many of the older ones are far more level-headed.
 * Its more likely that the issues with dragon behavior come from the fact that they don't receive the same cultural upbringing that humans do. Since most dragons (outside of China) are regarded as nothing more than military assets, they aren't given an education in anything other than what is considered pertinent to their usefulness as weapons. As a result, human concepts such as property, religion, race, nationality etc and all the cultural connotations that come hand in hand with them are absent from a dragons education and thus their understanding. The difference is demonstrated in the second book, where the main characters go to China and find that dragons are active citizens, because they receive the same education that children do upon hatching.

The United States will play a role in the series at some point
Important or minor, but I somehow get the feeling that with the fact that goings on in the Americas really haven't been mentioned in the series that much, there'll be mention of the US before long. Of course, we don't actually know if the Revolution was successful in this timeline, though we do know it happened based on Gentius' words in Victory of Eagles about "fighting the colonials near Boston". Then again, since the main British covert in the Americas appears to be Halifax and not Boston or New York, then it's quite likely that the American Revolution was successful. Could lead to some interesting events as the series goes on, such as the War of 1812 being fought with dragons as well and the United States becoming much closer to Napoleonic France.
 * In Black Powder War, one of Laurence's crew speculated the British may be retaking the colonies, leading Riggs to say it was more likely the colonials invaded Nova Scotia, which both heavily suggest the American Revolution was successful.
 * The Inca Empire is also suggested to be still around and may also play a role later.
 * As of Tongues of Serpents, the United States did revolt in '76 (and are making noises about a second war if the Brits don't stop impressment), but it's...different, and seems to have merged with Native American tribes, rather than displacing them (possibly due to their command of the vast numbers of native dragons and the colonials likely having one of their own).

The Tswana are going to help foment an early Civil War
With Tongues of Serpents, it looks like the U.S may eventually have to deal with a premature war, especially considering how one of the American merchants towards the end briefly mentions the division of slavery in the states (in a 'blink and you'll miss it' comment), as well as his own feelings about slavery. The Portugese merchant gets very irate over the issue and warns him that, yes, the Tswana might attack the U.S soon. Now, if the Tswana did get through their Roaring Rampage of Revenge down in Brazil and worked their way up to the U.S, attacking the Southern States over the slavery issue, it might add the right combination of fuel to the flame, along with the help of the small but growing abolition movement in early 19th century Reform Era America.
 * In addition, even in the early 1800s, there were a lot of early warning signs for the Civil War that did happen at about the setting of Temeraire, where states were threatening to secede over economics or tariff issues. Despite the U.S's Small Name, Big Ego status at around that time, it's possible that future books are going to explore more of the Americas and hit this issue as well.

The series will have a Distant Finale
It is stated that many dragons live for about 200 years. Using that logic, since Temeraire hatched in the early 1800s, he could concievably still be alive in the early 2000s. Don't know how it would fit into the context of the story, but it would be interesting to see if the rest of world history is any different for the 19th and 20th centuries.
 * Age shouldn't be an issue, Celestial's supposedly last well in excess of 300 years, possibly even 400.

Perscitia will wind up getting our heroes pardoned
In the sixth book we get a letter from England mentioning that Perscitia is getting herself involved in politics (whether the politicians like it or not). She will wind up getting people used to the idea of dragons as people, and force the admiralty to pardon Laurence on the grounds that he was simply trying to prevent them from committing genocide and turning the entire world against them. The admiralty won't be happy about this, but enough of them will realize that with the entire world going to hell having a dragon as powerful as Temeraire rotting in a prison colony is wasteful. They'll be willing to pardon Laurence just to get him back in the fight.
 * The hard part at this point would be talking Will and Temeraire into accepting it.

Temeraire is infertile
Seeing as there's only 8 Celestials period, and Temeraire did all that breeding in books 4 and 5 and never got an egg, he might very well be unable to sire an egg at all -- and Celestials may die out.
 * It's possible that Celestials can't breed with most other breeds of dragons. We know they can't breed with each other, it's not unlikely that it's difficult for the species as a whole to concieve.

The Tswana "reincarnation ritual" from book 4 is a Chekhov's Gun
Remember back in the beginning when Temeraire twirled about the idea of Laurence becoming a dragon after hearing that story? I'm just guessing that Temeraire isn't going to take it very well when Laurence dies, be it of old age or in battle if Victory of Eagles is any indication, but especially for the latter.

Laurence and/or Temeraire will be appointed Admiral of the Air
It will be brief though, and probably a measure of desperation in the heat of battle. Whoever is doing the appointing, most likely Jane or the Duke of Wellington, will have a hilrious short conversation with the two of them along the lines of, "You're a traitor, and you're a dragon. Unfortunately, you're both the only competent commanders on this field. Work it out, and we can handle the politics later."
 * Well now Jane is finally Admiral of the Air. Laurence is not the only competent air commander England has, as the plot of "Victory of Eagles" is basically "We'll stick you and Temeraire in the hinterlands on raiding detail while the real war effort takes shape". Laurence and Temeraire played a vital role in preventing French troops from foraging, but it was Jane who smashed the French attempt to build an air bridge, and Nelson who cut off French shipping in the channel.

Thoughts on the distant future (after Laurence dies, hopefully from old age)...

 * Temeraire, after a stint as Admiral of the Air, will take over training from Celeritas
 * Barring that, he will take a spot in the Foreign Ministry. At the very least his translation and cryptography talents will be of use once they get some magnification gear set up.
 * Emily Roland on Excidium will become Admiral of the Air, and be publicly female