I'm not sure how we're going to see Boreas validated. I mean, in what sense?
In the sense that the Dark Angels have become something they shouldn't be? I get that. That's a very powerful theme, but I have a feeling that we'd see the Warp freeze over in a novel before a Supreme Grand Master sat down with the entire Inner Circle of the Unforgiven and let them know it's time for a fresh start. That's part and parcel of the dystopian nature of Warhammer 40k.
In terms of Boreas's new sympathies and perceptions, though? His final message is to be sent to Astelan*, and I struggle to see how the Fallen represents a "better Imperium" or a "better Dark Angel". He is defined by controversy, he often contradicts himself, and he commits many of the same sins as the Chapter he hates... but in the name of a different ideology. I truly enjoyed the novel when I first read it, but the more I sat down with it, the harder a time I had understanding Boreas' evolving sympathies/sense of understanding.
* I'm assuming that none but the Supreme Grand Master could know of Luther - per the Codex - but Sapphon and at least two other individuals are shown as possessing that knowledge.
ANYWAYS.
Mr. Thorpe, if I recall correctly, you mentioned "Ravenwing" being part two to a trilogy of sorts that uses "Angels of Darkness" as volume one. Have you considered already what point of view you're going to use for the third volume (Deathwing, a Company Master, or perhaps someone else within the higher ranks of the Inner Circle)?