These were previewed in this Roll for Combat video from two weeks ago.
Transcription:
Updated Rules
The rules in this book are fully updated to work with Player Core, GM Core, and Monster Core. If you're using the Core Rulebook, Bestiary, and other older books, please note the following changes. You can find a preview document with the full details at paizo.com/corepreview.
Alignment has been removed. Followers of some deities can commit to being holy or unholy.
Attribute modifiers function like ability modifiers. Ability scores have been removed.
Components for spells and item activations are replaced with the relevant traits.
Elemental scamps have replaced mephits.
Genies have been reimagined to better match folklore. In this book are janns of all elements, jaathooms of air, jabalis of earth, ifrits of fire, and faydhaans of water. The ifrit geniekin are now known as naari. New genies of metal (zuhras) and wood (kizidhars) also make their debut.
Languages of elemental planes have changed to Susarran (air), Petran (earth), Pyric (fire), and Thalassic (water).
Off-guard was formerly known as flat-footed.
Munsahirs have replaced azers (page 131).
Planes include some new names (page 8).
Reactive Strike functions like Attack of Opportunity, but with a more descriptive name.
Spell rank replaced "spell level" for a clearer distinction from the level of characters and items.
Spell schools are no longer a part of the game, though illusions still follow special rules.
Vitality and void replace positive and negative traits and damage.
Wish is now a ritual, not a 10th-level spell.
All of these changes are honestly great IMO. They're mostly renaming, and as mentioned somewhere else ITT, it's clearly because of WOTC being absolute hacks with their licensing; Consequently, though, it makes all of the language so much more...natural. Clear, even. The few mechanical changes I'm sure will be well-received(dunno about the wish one, but the new ideas for genies, attribute modifiers instead of ability scores and ESPECIALLY removal of alignment are just good), so I think it's actually going to be a huge improvement, even if it was only out of necessity.
Honestly I'm kinda disappointed in this one. Not that they're doing it, that much is great. But the "just tick a box when you've got a half-upgrade" for boosts above +4 is such a lazy approach. It feels like a hack, because that's obviously what it is, and it's not something that they ever would have done if the system were designed with that in mind.
I'm not particularly sure what they should have done instead (they're the designers, not me!), but they really should have done a better job with this.
One suggestion I've seen made is the idea of just restricting the increase of any ability to certain character levels, much as becoming a master or higher in a skill is restricted to certain levels. That would've made higher level characters increase their less-used skills more than they currently can, without increasing their advancement in their primary skills. Which I haven't put a lot of thought into, but I'm not sure it would have been the worst thing in the world.
Really? They went with the most obvious and lame solution? Damn.
I do like the suggestion of restricting the boost the same as or similarly to skills, but regardless you're right - one is going to come across some sort of issue no matter how you do it, because they didn't design the game with that in mind. Perhaps it's the only glaring symptom of this change being sort of a last-minute get WOTC-off-our-backs?
Oh, I just realised where you commented! Here's the Lemmy thread discussing the full release of the 19-page rules update preview (sorry, the link is to the post on my instance, since Lemmy doesn't yet have a way to link to a post in an instance-agnostic way, like you can link to a community or user agnostically). Or here's a direct link to the PDF. It's not complete: so far they've only done enough to get you by if you're buying Rage of Elements.
There have also, of course, been multiple hour+ long videos from various creators (including former Paizo employees) discussing their thoughts on these changes, if that's your thing.