He's saying that you now have a reason to visit act 4 after you're done with act 3.
But there isn't. Act 4 is terrible for farming, and some of the mobs there are not worth the trouble fighting ( I am not saying hard - just annoying and maybe a bit overtuned )
Letting NV go across acts is a pointless addition because it only applies to playing forward through quests.
We need a waypoint system ( that would be unlocked once you finished the game ) so we can easily teleport between places in different acts. Otherwise, people are just better off staying in the only act that seems to matter - Act 3.
I've recently added Act 4 to my farming route after clearing act 3. Azmodan takes me maybe 30 seconds with the walking... and probably 2 minutes at most for completing the quest, identify and going to the next act.
I can charge up to 3 minutes timer on my Archon against Istaku. It takes me less than 30 seconds to do that. From that point, I usually reach Izual with the same Archon activated. Izual now drops more items (boss loots) and you may no benefit from Rakanoth's loots. The hell rift has an insane density of monster. The key warden will also give you additional loots for minimal effort. Your DPS is higher than mine. You probably could beat Diablo with a single Archon unless you backtrack a lot.
Unlocking WP and going wherever you want is not going to happen. This directly goes against their design philosophy. If you want to ask something more plausible, ask them for the option of picking the quest you want to begin the next act once you've beaten the act boss. You won't have to run through all the quests. You can just pick the last quest, do your run, and complete it by doing the act boss and move on to the next act.
It probably would save you a lot more time than getting 5 new stacks.