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.)
