All these new acts are actually "remixed" acts 1-5; you'll be going through mostly the same locales as you return to Wraeclast at the end of act 5, but they will look different, have different/new enemies and completely new story and locale progression to reflect your impact on the game world. This may seem lazy to some, but I think this is brilliant for a few reasons:
- From a game production perspective, this is a massive boost to production time, and it looks like the currently map exclusive tilesets they've added in Atlas of Worlds were actually made to be used in these new "remixes".
- In terms of story progression, as someone who's played through those three/four acts over and over again in the past years, I will be actually interested to see what happens in those places after the universe-impacting events in act 4 and (presumably) act 5, and I don't doubt that many PoE veterans feel the same way. (Again, to someone who picks up the game in 3.0 this may seem lazy - come on, I've seen these places already! Blatant asset recycling!)
In terms of character development, Wraeclast has become a significant part of the exiles' lives and it made them the god-slaying machines that they are, so it makes sense that they are willing to return to it despite escaping their exile in act 5 (and I assume that not everything is peachy in Oriath). I do wonder if there still will be room to explore more of the PoE universe in future major expansions, though.
- Two build defining moments currently revolve around having three difficulties and/or endgame - the bandit quest and the Labyrinth. Balancing those around two difficulties + endgame instead would've been pretty awkward, so they're doing away with the concept entirely since eventually eliminating difficulties was the plan to begin with.
It will be interesting to see how they treat Lab though, as you will still only return once to its location in your playthrough. I'm guessing they'll change it to three ascendancy points for act 3/8 lab and keep two points for endgame. People who hate doing Lab will be very pleased. Bandit quest equivalents will probably be in acts 5 and 8.
Also, the details of Legacy league have been all but confirmed. You'll be able to run three leagues at once! Madness! I sure am glad to be going softcore next league. What a brilliant way to salute this era of PoE.