I think more companions is basically a guarantee. Whether just the ones that have ben datamined or more.
I think there's a decent chance that they'll reveal maybe one extra sublcass not from the player's handbook for each class. No extra classes though, that's something for DLC (also I'd be shocked if Larian weren't at least considering creating their own entirely homebrew class for the game that they'll release as DLC down the line. Don't know if it'll happen, but I have to imagine the idea has at least come up.)
I do think that act one will change somewhat. Not radically, but maybe a couple more quests, or some quests getting more options.
