The game is designed so players have to compromise. Unless Larian changed things from stuff I datamined a few patches ago, but back then I really doubted it was possible to bring everyone to act 2 because of the disposition system, some camp cutscenes where someone can dies/leave and some personal stories clashing with other quests.
Also, some people have this idea that an evil character would follow the path of joining the Absolute because it is the evil path. But this isn't an organization, it's a religious cult. Joining them means converting to the Absolute as a god. Not every evil characters would want to do that. Faithful evil clerics/paladins should be all over the plans to destroy the cult.
And since now we have non-origin companions, I wouldn't be surprised if there was a few more available past act 1, especially if you follow the path of joining the Absolute cult (which is something that is hinted at being more than goblins vs grove) since most known companions will be against the idea. But I do not expect that many more. Probably two, who slot in for Jaheira and Minsc.
But that is if the Absolute doesn't try last minute temptations. Take Wyll, what happens if the Absolute propose to break his contract with his Patron and give him power instead? Gale and his chest problem? Astarion and his sunlight?
I think Shadowheart and Lae'zel are the only incorruptible there + Jaheira and Minsc.
Other things that Larian is keeping secret:
- a building in Baldur's Gate for resting in instead of an outdoor camp once we get access to the city.
- more custom Tav VO (there are actually more in the games file already).
