Nicely put together! I can always appreciate good formatting. I appreciate this is old, but I really like a lot of what you're doing here and had to give feedback.
Expanded Librarium is a neat way to give Blood Ravens the psychic depth they're always claimed to have, making them
broader psykers now that "Chief Librarian" is a universal upgrade. However, it seems more complex than it has to be; why not just reverse the order of operations? Let Blood Ravens add the PSYKER and LIBRARIAN keywords to any BLOOD RAVENS CHARACTER for a set points/Power cost, which comes with a Psychic Hood and the ability to manifest 2 powers, deny 1, and know Smite + 2 others. Or make them weaker than "regular" Librarians, only able to manifest/deny 1 and know Smite + 1 other, to emphasize "real" Librarians as specialists and encourage lots of cheap psykers in the Blood Ravens' ranks. If you wanted, you could expand it even further; take a page from the Deadly Pathogens rules, and let Blood Ravens upgrade "BLOOD RAVENS models that have the word ‘Sergeant’ in their profile", like Thousand Sons or Grey Knights. That might be a bit much, though.
Two big thumbs up to the concept behind
Steel Rain; it really emphasizes the Blood Ravens' talents as cunning planners who launch near-prophetic strikes, while also referencing a much-loved meme. It also benefits a fairly broad range of units, even without Strategic Reserves; Drop Pods, Terminators (potentially twice per battle!), anything with a Jump Pack, Reivers, and all Scouts variants. ...kinda weird that Marine AIRCRAFT don't have Death From Above, honestly, but I'll roll with it.
I'm not so sure about the execution, however. Comparing it to existing Doctrines...
Other Doctrines are pretty broad. They benefit all melee attacks, or all Heavy weapons, or all attacks against CHARACTERS, etc. This is a very specific Doctrine; it only affects units deployed in a particular way, many of which will cost CP to do, and in fact you're limited to less than half your army doing it anyway, in Matched Play!Other Doctrines are comparable in terms of power (about half a Chapter Tactic, basically), but that narrowness makes it feel much weaker than it is on an individual level.Other Doctrines are all, without exception, offensive in nature. Just like the core Combat Doctrines, the Chapter Doctrines help you hurt stuff in that phase; this one is the only defensive Doctrine, which makes it feel weirdly passive and easier for the opponent to ignore. It also doesn't fit the described flavour.
My suggestion would be to make it an offensive bonus, and a broader buff that you access by setting up a unit in the Reinforcements step. Perhaps make it an aura that buffs ranged attacks made against enemy units within X" of such a unit; that way you can get a lot of bang out of just a few Reinforcements units, rather than needing to shove half your army into Reserves,
and you're encouraged to think carefully about spacing your reserves for maximum effect. Something like:
Steel Rain
While the Tactical Doctrine is active for your army, each time this unit is selected to shoot or fight, you can re-roll one hit roll or one wound roll when resolving that unit's attacks, if the attack targets an enemy unit within 12" of a friendly BLOOD RAVENS unit that you set up on the battlefield during the Reinforcements step of your last Movement phase.
Never been a huge fan of
Relentless Seekers - it always felt like a bit of a damp squib - but I appreciate why you're keeping it intact instead of changing it up.