Edit: Ok, bigger wall of text than I thought I was writing. I apologize in advance!
I'm with AndrewChristlieb in terms of his general sentiment that the Inquisition should be a series of reserves options and scenario ships, rather than a full fleet list. Totally going to catch some flak for this next bit, mostly because it's an interpretation of lore (and therefore inherently subjective).
I'm not even completely comfortable with Space Marines having a whole fleet list. Yeah, I said it. In the lore, you rarely see more than a single strike cruiser or a battle barge with a company, rarely more onboard, responding to strife on a planet. I can see escorts having a role alongside a battle barge (who's going to send something that big in without any?), and can even more easily see small task forces of marines (maybe a handful of squads) deploying to a warzone on a Gladius because that's about what they need for transport. THAT SAID, I'm happy we have the fleet lists (standard and dominion) because (A) they've helped identify weaknesses, (B) allowed us to grow and develop the concept of a "strike cruiser" into a class of vessels instead of a cookie-cutter ship, and (C) allow us to represent truly monumental undertakings or even roving crusade detachments (I can easily see a Black Templar Crusade deployed across a pair of strike cruisers and attendant escorts; that's a good example of where the lore would support a Space Marine fleet list, tbh).
How does this matter for the Inquisition "list"? Well, everything that applies to Space Marines, goes double for the truly specialist forces. I figure the Grey Knights probably have the luxury of sending their people around on strike cruisers and battle barges exclusively, and probably have a big enough fleet between the shipyards of Mars and Jupiter relative to the number of Knights in the field at any one time that they can afford to dispatch a handful of squads on a ship that could comfortably billet one hundred marines. That said, you'd have to bend yourself over backward to try to create special Grey Knights escorts, and ultimately they'd just end up being overly expensive versions of Gladii, Novae, and Hunters, so that's not really worth the effort anyhow (and I'm assuming you wouldn't bother anyway). As for the Deathwatch, the lore, at least as it's laid out in the RPG books, supports single-squad deployments on Gladii and Hunters to various warzones, in rare cases you might see enough Deathwatch brought together for a mission to warrant a strike cruiser. I'm actually planning on painting up a Deathwatch strike cruiser and in my own internal debate decided not to bother with any special rules for them as the number of marines deployed on the ship would be so few relative to a full marine company on a strike cruiser that I figured it would simply average out to a "standard" marine strike cruiser in terms of bonuses and benefits anyway.
What I'd really like to see would be a "list" of reserves options with perhaps special rules (like "you can take a Black Ship to replace a battleship in any imperial navy list") for the Inquisition. I don't really see too many Inquisitors having the patience or the training to orchestrate a void war, and they'd probably leave that to the commander of whatever battlegroup they hijacked, while worrying about their more focused goal (whether it be a "board the enemy ship" subplot, Exterminatus, or commanding a planetary assault). On the other hand, I'd like to see a Sororitas Monastery Ship perhaps, although an astartes strike cruiser would probably cover that pretty well.
Also, as an aside, in
Faith and Fire by James Swallow, the Inquisitorial Black Ship had a detachment of Sororitas onboard for maintaining order among the inmates. That puts near-astartes defensive crew onboard, though I'd still see them not performing boarding actions as their purpose was solely to defend the ship and its cargo.
I'd also like to see Adeptus Arbites vessels too. I really enjoyed the Shira Calpurnia series by Matthew Farrer (
Enforcer is the omnibus) and I'd really recommend them as reading to anyone who wants to see what Hydraphur is like or how the Arbites interact with various Imperial institutions; he did a great job. In that book, Farrer gives us Arbites-crewed intra-system corvettes and customs vessels (easily represented by defense monitors, I realize, but perhaps there's room to add more life and color to BFG?), and somewhere I've definitely come across a "Mobile Arbites Precinct" cruiser in the lore, which IMO would make a great addition to a scenario.
Ultimately, I feel like the Inquisition and other Imperial forces are better suited to scenarios and sub-plots than to a tournament list. I feel like we have the opportunity here to, instead of adding one more tournament list to the game, really add some depth to some of the battle scenarios or add new sub-plot tables and the like. With a "Pax Imperium" mini-supplement, we could add some interesting narrative gaming options that, while they wouldn't be standard fleet stuff, would still hopefully be attractive to gamers.
In case you're wondering, I'm putting my money where my mouth is and volunteering to be a part of this if people like what I'm suggesting here
