Bit off topic, but might as well add the last bits that I know of from the datamines:

Nightsong, originally, was "Shar's penitent. Cursed to bear the loss of all those who worship her."
And during Act 2, it seemed that we would have been able to side with Ketheric or the Nightsong in some fashion and one path would've had her as a boss fight.

Chubblot has some more stuff in one of his vids and has some VO'd Nightsong dialogue in his "Voice Lines: Cazador/Raphael as a Cambion/Mizora/SPOILERS" video.