Honestly I'd prefer a move towards the 19th rather than 18th Century. Much more eurocentric, considering the main hallmarks of the 18th century were piracy in the West Indies, the Seven Years War which was global, the American Revolution, and the French Revolution which spilled over into the 19th Century as the Napoleonic Wars, which were Objectively better than the Revolutionary Wars.
The Empire evolves from a feudal system to a unitary state, and they give up puffy sleeves for pickelhauben.
Bretonnia, either a fucking French Revolution because they're French so they must have a revolution because that's what the French do, they carry on business as usual with knights and shit, or they become sort of a mix of the two, like how Khador is a mix of Tsarist and Communist Russia in Warmachine.
Dwarfs carry on as usual. They augment their defenses with technology, but they use outdated tactics on the battlefield.
Nobody cares about the unimportant nations like Estalia and Tilea, they're irrelevant. Kislev, we could do something with them, maybe the Vampire Counts got chased out to here and they took over. Talk about hemophilia.
Orcs... Are orcs, but with gatling guns and revolvers. Same for ogres.
Chaos is behind every other revolt, but not the hypothetical Bretonnian one.
Beastmen that aren't chased out of the Old World are negro slaves to the Empire, so the rest of them are super pissed.
Chaos is Chaos, now with guns. They had a brief stint like two hundred years before where they successfully held most of the Northern Empire, but then Everybody kicked their asses (Except Araby, because they're heretics).
Elves are the same. Dark Elf attention has turned to the Southlands where there are Imperial and maybe Bretonnian colonies that are easier to raid.
Skaven are still dicking around and have dug to Australia. Meanwhile, the Empire sends convicts to Australia to work in mines. Birth of the fantasy German Australians.