Don't forget that DnD has NINE alignments and all of them are different. So even if there will be only 2 voices, they have to record different voice reactions to the same situations.
I still don't understand the significance of this. Why do different alignments need different voices? Are the evil voices going to have an evil laugh after every sentence?
Also, I wouldn't be optimistic expecting that alignments will be implemented at all in the way you seem to be expecting. I doubt the player characters will have anything resembling a clear alignment. The best I can expect here is that Larian might use the alignments for some flavour in quest design. (And that's fine by me.)
They rather need other intonations and phrases. Now MC has a lot of sympathetic and kind phrases in the game. The difference is obvious. When MС sees the dead fishermen, she/he says with a sympathetic "no luck" . What does Astarion say? "Mmm, what a waste of blood."
Astarion is an evil character, you can see that right away.
Even in the first act, there are enough short phrases that might be unnatural for an evil character. For example, pity for the tieflings in the dialogue with Lae "They are not warriors , do not be so strict with them". Hey, am I going to kill them? What are you talking about? MC? So yes, it's a bit sad.
