Looking at the cover art, it looks to me to be a portayal of civilian, ganger, ruling caste - I would guess this social cross-section will be a common cover-art format across these house books.
The trailer:
Seven seconds into the trailer vid, there is a section of text visible (word fragments in parentheses are my own best guess):
Not much at all to go on, but that reads to me like an ogryn hired gun. I would expect a few Goliath-themed or ex-Goliath characters like that as an effort to sell it to all players. The ogryn servitor sketch from the gangs book was labelled as "Sparky" so this may be an expansion of that character, either as a hired gun or maybe a named brute. But perhaps it's a sample background to go with expanded options for (or if we're unlucky, a rewrite of) the servitor ogryn. My money would still be on a hireling though.
At 21 seconds, the fat crowned Goliath image is I suspect the ganger-turned house master, Hectork Scrak. But whether he will be the king referred to previously, I wouldn't want to guess. Personally I dount think Slate Medena has been popular enough to warrant other "heroes" being released as a priority.
The models:
I'm not so sure that stimmers and prospects will be on the same sprue. For a standard box, there'd certainly be room for one stimmer and two prospects per sprue but if so then we have likely seen every weapon and head option these models get in plastic. Thorgor you're probably right but I'll hope for them being separated though, probably in packs of two identical sprues for £10-15.
As to those indeterminate guns, I'm in the grenade launcher camp; belt-fed is no great difference to drum-fed but maybe they get to re-roll failed ammo checks due to the amount they're carrying in those massive drums.
Wild speculation: maybe they're heavy grenade launchers that get Blast(5"), or rapid fire for absolute filth! Perhaps what stimmers get is access to twin-linked special weapons; that way they're still able to move and fire (the body pose doesn't suggest Fire(Double) to me), and also aren't treading on the toes of brutes like the stig and lugger with their big guns.
Meanwhile the standard renderiser doesn't have a circular saw blade at the tip, so it's possible that those melée weapons aren't unwieldy but probably are restricted to stimmers only.
Assuming the gang hierarchy set-up hasn't changed, I wonder if prospects won't be a form of hanger-on (that allow for 2 with one 'slot' maybe, or just have unique weapon access). Otherwise they could be a (very cheap) hired gun that have to pick from a small HWL as appropriate - fluff-wise we know they're trying to impress but there's nothing about a gang ever letting them in. Either of these options would place them below juves in a hierarchy.
Alternatively, maybe they're just a form of juve that evolves into a ganger. Again that would place them below the current juves. Maybe you will need half the gang members to be gangers and prospects going forward.
House Alliances:
To be honest, I'd expect this to largely be which clan houses can ally with each other (and why Orlock/Delaque won't happen), with perhaps a campaign event table to provide varied combinations: this week Delaque and Escher can't fight each other without being penalised in the post-game sequence or something. Or enmities, such that affected gangs get bonus XP for fighting their given rival-of-the-week. Maybe linked to the new scenarios, if those aren't just re-skins of existing ones.
Slave Ogryns, sub-faction gangs and future books:
The ogryn gang worries me, mostly because if they are an attempt to shift existing 40k kits then in my view it gets risky. Arcoflagelants for Cawdor and skitarii for Van Saar doesn't seem too bad at first blush, and maybe tempestus scions representing road-guard elites for Orlock. But if this is the case, what do we risk getting for the Delaque and Escher? I suppose admech sicarians are/were assassins so could fit in with Delaque's sneaky theme. For Escher however, all I can think of in a similar vein would be dark eldar wyches or harlequins.
Hopefully my fears are unfounded though. In which case Spafe's list seems pretty comprehensive; the only things I can think to add would be ash-waste/shanty gangs to Cawdor (at least until they get around to an ash waste expansion proper), with hunting parties or chem-soldiers for Escher, recycling the idea of gland-war veterans from Inquisitor.
But at that point, most every sub-faction feels to me like model options would be covered by a conversion kit for the parent house-gang models, if not just left to players. Redemptionists would only need more pointy hoods and nicer guns to go on the Cawdor plastics (if the Red Redemption is still wealthy now that Cawdor is the poorest clan house), while the Abominable Intelligences of Lord Otto Van Saar could be made by just sticking with helms on the existing Van Saar models. Which would make ogryn gangs (whether led by a human or a bone'ead) a real oddity and potentially disappoint fans of the other houses later on.
Bikers for house Orlock are unlikely until an ash waste setting, I think - if only because it reduces the amount of terrain you want on a 3D table and would be really awkward on the ZM tiles. Servitor squadrons could be a thing though, given the Lugger brute. Meanwhile their new champs might have servo-rigs as standard since industrial-tech seems to be their flavour now, while prospects could be mining helots with las-cutters, grav-guns, ore-grinders and the like.
I struggle for champion and prospect ideas with the other houses. Cawdor getting a preacher/deacon/zealot (with eviscerator!) would be fairly obvious and allow for a Redemtionist flavour to standard gangs, maybe prospects with tox bombs and/or chain glaives. Maybe inventor types for Van Saar with experimantal weaponry - hopefully just guns not available elsewhere, rather than random profiles or upgrades to range, armour pen etc. that can be bought (just because some combinations would be bound to end up hideously under-costed). Escher could perhaps get a beast handler that gets common access to phyrr cats and maybe an extended range on them, otherwise I've no clue. And all I can think of for Delaque would be access to a super-sneaky sniper gun or else a minor wyrd for their champion. And I really hope it's not another psyker, even if they get the Immortal Cult as a sub-faction gang.
One thing I do note is that there was some word-play on "spyre" on WarCom last year but with these new house books, anything spyrer-related has presumably been pushed back. My suspicion is that the brutes were all supposed to have forgeworld offerings either released or nearly so by now, and delays there have caused a knock-on effect (I just can't see plastic spyrers being financially viable, unfortunately).
Do people reckon these house books will follow the same order as the original releases? Or is there a consensus that Goliath was just the least popular house and are getting boosted first as a result?
