Yeah I think the "book covers" are trap doors. The Golden Shields bear the crest of the Raven's Veil so they along with the Crescents and Masks--which I mistook for bones, are clearly part of some "token" system that we don't fully understand yet, and may be used in connection with the tiles bearing the faces of the Cadre members along with the "mystery" she-elf with the dirty face--the one who is cast in blue plastic and bears the knife chain weapon thing and appears on the front cover attacking the Elf hero.
10 Quests, and probably the first 3 will be you as the Knight seeking out the various Cadre of the Raven's Veil members. Perhaps you are recruiting them, and perhaps there is some perk later for doing this rather than skipping straight to the group quests (again, assuming a template similar to Frozen Horror and Mage of the Mirror, but hopefully with better playtesting). The idea of scalable difficulty might be pure fluff/hype, but I think they are setting it up so that perhaps these guys will be more useful as hirelings if you play these quests. Maybe they get bonuses (not just a discount) or perhaps the Knight gets to hire a certain number of them for free. Then again there are only four, and no other mercs are included. Will the blue elves be hireable too?
MOTM encouraged you to use other mercenaries in the group quests from other expansions you might own, so that right there implies the Cadre members (all four of them) could be used as well as the 12 Men-At-Arms from Frozen Horror in those quests or in Mage of the Mirror as well, if you own them all.
Probably the "Alchemy" deck (glad that is now the official name!) will probably also be something they encourage us to use in other quest books besides this one, which would be pretty cool. Since they're giving us this deck (which works in conjunction with stuff you find in the Treasure deck) it would seem they won't give us a regular Alchemist Shop with Equipment cards for potions this time, since this kind of takes the place of that. But theoretically you could still buy potions from other expansions between quests, though they haven't stated that yet.
The Sinestra ghost figure is the "Dread Wraith" which is also transparent plastic like the Specters and there's only one of it. It takes up two squares so it's not the size of the Frozen Horror but certainly a "large" monster like the Giant Wolves. It could be that the "wraith" is actually the cloud figure and the various "faces" inside it (Sinestra, some other random elves, humans maybe and perhaps even something that controls Sir Ragnar which is my pet theory but is unproven) are other characters.
The blue figures all seem to be bad guys... perhaps the female Elf with the Knife-chain is a turncoat member of the Cadre or something? There's two of her though.
The "tomb" is probably something else. We've speculated that perhaps it is like Galadriel's Mirror in LOTR (a magical basin into which water is poured and then you can see other places, timelines, persons, etc). It appears to be a molded piece of gray plastic with a piece of transparent plastic that slots into it to give the illusion of a "watery" surface.
We get two more "door bases" (plastic into which you slot the "mirror" tile)... so very easy to mod those with your own cardboard to add more open doors to fix those Frozen Horror quests that call for too many.

One of those tiles appears to be showing an image very similar to the back of the "Dread Spell" card ("chaos" magic in the old game we'd say). So it's a gateway to chaos or something that produces evil power?
The "realm of reflection" was mentioned in the original MOTM. The grassy stone garden area looks like a "reflection" of another kind, like a place of rest, or perhaps like an oubliette. One wonders what is on the back.... of course it's always possible they just put the same image (or plain black) on the back of these tiles, but hopefully it's something else cool on the other side we just haven't seen yet!
No Sir Ragnar... not even a tile for him yet. So I guess he'll just be a character that gets mentioned but is never seen on the board like the Emperor (King in the remake), Zargon, Mentor, or a dozen other characters from the lore. Then again there are four "cultists" that have the nostalgic pose of the original Chaos Warlock (and gray color) which could be a stand in for other characters (or they'd just use the Dread Sorcerer from the game system to represent Sir Ragnar... I bet the companion app would ask you to use that or the Sir Ragnar prisoner figure if you own the Haslab version even though he doesn't look exactly like the cover... prisoner... hmm... still makes me wonder if he's a "prisoner" being controlled by magic rather than just an evil traitor who did it for money/power, not saying he has to be but still, "Command" is a thing).
I'm a little disappointed that there are not going to be more of the Elven soldiers we saw on the cover. Two of the "Big" armored dudes, some repeats from MOTM, but no spearmen. I guess this time they were going for variety. I am sure the box images are final so no more surprises inside. If they have an "outer box" alternate cover like MOTM it won't show us anything new in terms of contents I predict. Yes, Rogue Heir of Elethorn had some additional lore fluff on its inner box but no hidden contents.
Any "box teases" or misdirections would be to fool us in the lead up to the release, they would serve no other purpose for people buying the product a year from now.
So all that remains are the rest of the cards: stats for the characters that we haven't seen yet (we can assume the Elf Warriors are the same as before, and the Potions are probably going to be mostly repeats of what we have seen in past releases with slight tweaks) and the mechanics of how the various tiles and tokens actually work... plus any rule changes in the Quest book itself.
What will the difficulty be like? I predict it will be a difficult pack, but aside from any scalable options in the early quests, we don't know if it will be as (broken) as EQP, hopefully not. If it were on par with the difficulty of the Mythic questbooks, that would be fine (maybe less of Joe's and more like Teos and Stephen's).
So no character pads or special dice this time, our "surprise bonus" is the Elven furniture which appears to be trying to fill out the replacement set of stylized furniture from the Game System with a new aesthetic. Table, Sorcerer's Table, etc. but why no Torture Rack? These guys are evil but not evil enough? (Unless that magic mirror serves that dual purpose... yikes). Not saying it has to be for "mature audiences" or anything, but why put the 14+ and then sanitize it as if it's for today's 10 year olds? Sorry to get off topic, not gonna rant about that.