It's a little difficult to say, as Ex3 is still in it's early stages and all of the splatbooks released so far have been focused on the mechanics of the game, not the setting. There are a few things I can think of off the top of my head though.
There will be new types and new factions of Exalted, though details are still sparse.
- Liminal Exalted: think Dragon-bloods but for the Underworld. Also they are zombies and increase their stats by using body parts. Need better Dex? Go find a dancer's legs. Maybe similar to how Alchemicals can swap out their builds?
- Exigents: the Exalted of small gods, these are unique beings as the average harvest god does not have the strength to survive the creation of more than one Exalt. They also need the Unconquered Sun's permission and a piece of his power to catalyze the process. There are hints of a black market for these pieces.
- Getimians: Either rouge Sidereals or something entirely new. Very little is known at the moment but they oppose the very concept of Fate, have their own internal Looms of Fate and were founded by Rakan Thulio, a first age Sidereal.
That's the only big stuff at the moment but so far the current state of the lore is that your GM will be have to make most of it up themselves or rely on previous editions.
There are massive geographic changes to the Northeast and Southeast, a new large island in the Southwest and all of the coastlines have been redone. A bunch on new cities have been added and minor changes have been made to returning established locations but their relevance will depend on where your game is set.
There are some changes to the early history of creation, the books go out of their way to avoid using the word 'Primordial', instead going with 'Enemies of the Gods' so presumably the original Exalted were pitted against more than just the Primordials. After their victory however the Exalted turned on each other, not much is known yet but out of this conflict some Solars and Lunars made a series of political marriages that became the origin of the Solar/Lunar Bond.
There are a few things that will probably lead to larger lore changes once books more focused on setting are released
- Exaltations only seek "Excellence" in their host regardless of morality so the Solar: good, Abyssal: bad dynamic is no longer a given.
- Speaking of; Abyssals might actually be interesting to play now, Onyx Path seems to be committed to actually making the Abyssals the Exalted of the Dead instead of the Exalted of Slaughter. The Deathlords and Neverborn will have a much lighter touch this time around
- Lunars seem to be a fusion of their 1st and 2nd edition themes: a lot more anger and war but still protection and molding societies. The Wyld doesn't seem to feature in their lore nearly as much either, For example he breaking of the castes was a deliberate move on their part and there has been no mention of chimeras.
- Dragon-bloods are much more spread out across the world, with clans and even entire civilizations unaffiliated with the Realm or Lookshy in every direction.
It's entirely possible that absolutely none of this will have any impact on your game. I may be able to answer more specific questions but that's all I can think of at the moment.
