How much have the aethers changed since Aether of Night?
The big change I made to the aethers, other than adding this other world... A couple things going on with the aethers.
First off, when you finally meet people who bear the aethers (which we're calling aetherbound, currently, and I like that term), you will find that, in order to differentiate them from things like seons and things like spren bonds and things like that, I've decided that one core aether bonds a lot of people, and it's one entity that you are all bonding with. So, if you meet five aetherbound who have bound to the Verdant aether, they are all bound to the same individual, at least on the core aether world. And that just adds a different nuance to it. There is lore and worldbuilding that is different that I will leave. There's a lot that's the same; there's a lot that's different that I'll leave to you to discover. I am working quite a bit on this planet for future projects (which, no, I haven't secretly been writing yet). But that's the big change.
And the other change is that I decided that aethers would be able to... I would have different things happening with them, different strains. In their own lore, they were not... the aethers themselves don't believe they were created by Adonalsium. And so they're, like, a different sort of thing, a different entity, so to speak. And this goes back, even, to way back when I tried to write them into Liar of Partinel, them predating things like the Shattering and what not, and it feels right for how I want to treat them.
Those are a few little tweaks that you will eventually get. But the basic mechanics of how they work is the same as they worked in Aether of Night. I think that one of the things that really worked in Aether of Night was the mechanics of the aethers. I thought they had a lot of interesting storytelling play, I thought that they did different things than some of the other magics that I was writing did. And they have remained solidly a part of my brain for how the Cosmere will proceed. And that's why you see Mraize having a chunk of an aether and things like that in his trophy case.
We know there are multiple planets with aethers, so do both of these worlds exist simultaneously? Or is this one an evolution of The Aether of Night's Vaeria?
They do both exist simultaneously; this one came from that one. The answer to both is "yes."