Okay so I'm just going to think on paper about the ToV postgame world.
No more blastia. Shittons of technology was based on blastia, so there's a temporary lack of pretty much everything.
But! The spirits. The party ended up converting all those blastia into spirits. Now, when the party created the elemental spirits, they were using complete apatheia at the appropriate aer krene. But the massive army of spirits created during the end had neither advantage. Each spirit was created spontaneously, from a fragmented apatheia, with a formula engraved on it.
The result? I'm inclined to think that the resulting spirits are mentally fragmented, and are capable of little more than the function they performed as blastia. So we get an army of spirits basically doing the same job they did as rocks.
But according to the game, all the blastia cores did was convert aer into usable energy, which the rest of the blastia would then use to do its job. But the formula on blastia differs, yes? I'm most inclined to think that the spirits would simply have to be equipped with technology if they wanted to continue to perform their duties, but I need to clarify my thoughts and examine canon. There might not be a single perfect answer.
Moving on. I can only interpret the ending to mean that Witcher harnessed electricity during the postgame technological revolution. So those spirits unwilling to work as aer converters would be less necessary in any case. With an understanding of electricity, no doubt blastia could be converted into simple machinery with relative ease.
Politically, the Union and Empire are, I believe, working to unite under a single banner. This is occurring at the same time as the technological changes in the world. Leadership-wise, the Empire obviously has Ioder, a child king, and Flynn, who has built up a reputation as a hero and true knight. The Union meanwhile has Harry, who is becoming a child leader to match Ioder, and Raven, the charismatic righthand man with street cred for betraying the knights, and potent battle strength as a result of his work in the party. Strong leadership combined with fear and unrest could, ideally, make the unison of parties go smoothly.
Incidentally, the main reason Raven's heart wasn't converted into a spirit is because it wasn't hooked into the blastia network that Alexei began and the party perfected. The reason it didn't need to be converted was because it didn't use aer anyways. It used the life force that would normally power his heart to function as his heart.
Anyways. That's pretty much all I got logistically. There's a few other things, like the bodhi blastia spirits doing the "contract" deal with their users, so the party/other people still have superpowers. And there's the fact that, without aer overflow, the monsters would die out, leaving only normal animals. Or at least, the monsters would turn nonviolent. Duke's nature communing scene is a sign of this.
I think that's it? More to be added, I guess. I haven't done my character thoughts but I have those typed up elsewhere.