Narratively, the whole "look what you did!" theme for Act 5 thru 10 makes a lot of sense.
The first three acts are a natural progression of Dominus and Piety's scheming/experimenting. Act 4 digs deeper on what (who) was influencing Dominus/Piety to start digging up old relics and messing with ancient magicks. The why is a little more questionable... were they feeding energy to Malachai, knowingly or unknowingly? If Malachai was slurping up enough mana to suppress gods, what real use did he have for the vitae of mere mortals? (had to be chump change, in scalar comparison)
Act 5 is a very reasonable next step. You killed the High Templar (theocratic El Presidente), and nature abhors a vacuum, especially a power vacuum. Oriath was your home once upon a time, so not letting it go to shit makes sense.
The basic framing for Act 6 and beyond is also reasonable, on paper; Malachai was suppressing the old gods, and killing him let them out of their cages. The real trick will be the narrative glue they use to bridge the gaps.
Mechanically, I can't really say I'm thrilled or surprised with the cruising altitude view of design choices. Path of Exile: Super Turbo Remix Edition is basically what I've come to expect, based on what they've actually done since late beta.
The Pantheon buffs are straight up Ascendancy: Remix Edition... the buffs are independent of character class, and tied to decentralized boss kills as opposed to just killing Izaro (multiple times).
Acts 6 thru 10 seem very similar to what GGG did with the map refreshes that came with Atlas of Worlds; take the existing parts and recombines them in new and (hopefully) interesting ways, with a little bit of truly new stuff to multiply the possible combinations. In the ZiggyD clip, there's a bit about revisiting the Prison in Act 6, and a double boss fight therein. (Shavronne + Brutus simo) Atlas saw at least a few combo boss fights; souped up bosses with serious blue/yellow supplementary summons, Marceus/Goddess/undying-hammer-dude, two/three-rogue-exiles-simo-as-a-boss, probably a few others I haven't reached yet.
I feel like multiple behind-the-scenes things are happening with the whole six-acts-at-once bit...
Firstly, it's a big goddamned spectacle and a total PR coup. GGG has leveraged their position into an Xbone deal, and the Oriath xpac just magnifies the console release's momentum. While I'm very cynical about marketing generally, I cannot deny that they really hit the bullseye this time; the buzz has been hella positive and the hype train is very real.
Coming up with truly new ideas, both narratively and mechanically, can be really hard. Shoehorning them into an existing framework can be harder still. By sorting out the Whole 10 Acts and No More Do-It-Again Difficulty Levels (mostly) with the remixing method, they are putting themselves in a better position to give new ideas their own room to breathe. I would not be at all surprised if the post-Oriath content reveals a M:tG-esque Many Worlds cosmology... it would put a tidy little bow on a lot of the elements so far. "Yeah, those gods? Nah, not really gods, just super powerful assholes from Elsewhere. Those weird demonic fuckers that keep showing up here and there? Also assholes from (Really Weird) Elsewhere. Those maps y'all keep fussing with? Smaller pockets of Elsewhere. Speaking of Elsewhere, there's a cry for help coming from..."
The inner circle of GGG has been working on this game for 10 years... that's a long time to be on a single project. It's reasonable to want to cash out on the sweat equity, whether it's to retire or to just do something different. Having a good point to hand over the reins makes it easier on everyone. The console release + completion of the original vision of 10 acts seems like a good point to me, if that's something they wanted to do.
Most of my actual questions at this point are pretty minor, and all boil down to the proper details re: the refactoring of existing content/rewards.
Most quest rewards are easy enough to move around; bandit bonuses are the only big question mark.
Labyrinth access... just cut it down to three passes? Seems the simplest solution. Get 3 pips on normal initial access, 3 pips from Act 8 (Act 3 revisit), and 2 from Endgame Labyrinth from maps.
When are maps going to be available? My guess is Act 8, with maybe a small adjustment to effective area levels, no other major changes. (maybe 6-10 new mid+ tier maps, remixes with the new tilesets)
How are low-level / high-level prophecies going to be keyed without difficulties as delimiters?