As the first truly "original" larger box retail expansion for HeroQuest in over three decades, a lot is riding on this release being a success. They can't coast on the fumes of our good will for this one I think, but they should be able to pull off a success. Prophecy of Telor is close behind as a sought after exclusive from the Haslab campaign that will surely be a nice backstop if it is less than thrilling, but HeroQuest still feels like a risky niche portion of Hasbro's revenue stream and my fear (diminishing by the week it seems) is that the company could drop the hammer on it at any point if they don't find it profitable and we go back to being a fan community without corporate backing once again (which we can do as long as we want). But they want mainstream success so I am sure they're not being careless here. And yet so much is being kept secret with not much time left before release. Playtesting internally is essential and they'd be foolish not to, at this stage.
IF they follow the EQP/BQP template of 10 quests, split into 3 solo quests for a single hero and the rest being group quests (with an extra difficult, long "two-parter" for the finale) they will be limiting themselves but the challenge to make it more playable out of the box without fan modding shouldn't be that difficult. They already have had the experience with two legacy packs to see how the community reacts and how they can work around the problems in those products.

Do I believe they will do Scalable difficulty? Absolutely. It would be so easy to implement, and they are claiming they will. We already know that EQP & BQP claimed to be ready for both brand new HeroQuest players with basic heroes (the solo quests) and experienced players continuing with (obviously well equipped) characters to be challenged. Out of box in 1992 they clearly failed at this... the solo quests are way too hard as written for beginner players and are challenging for a well equipped solo character. Into the Northlands and the EQP remake updates made these a little better but their solution was to just give you more opportunities to get gold before the hard quests began and a few more rewards IF you happened to survive those trials.
They already have planned a "Prequel" quest for GenCon to the Rise of the Dread Moon in early August, which could easily serve as a "patch" after getting feedback from fans after that first month or so after release. But I think it would be short sighted of them to rely on this "prequel quest" to fix another broken pack in terms of difficulty.
All you have to do is throw a line or two in there about if it's a new character or a hero who has completed several quests already and has a supply of gold, potions and equipment there are different outcomes. You can increase the rewards in quest notes for the in-experienced character. This is a super easy, brain-dead simple fix, so if they don't already have some amazing scheme like the multi-color monster systems on at the Inn, I would be shocked if they didn't deliver on this "promise" from the early developer diary with Doug Hopkins.
So I'm imagining they could have a symbol for indicating a newbie player and another for an advanced player. Put these next to the quest notes. Maybe double it? So the beginner player gets two healing potions while the advanced player only gets one. The beginner player gets 200 gold coins and the advanced player only gets 100. Or something like that (it could be triple or quadruple for all we know, they are building this one from the ground up).
IF they follow the template of having 3 solo quests in which a character is meant to go from beginning equipment to max equipment by the end, that can be accomplished, but they would also want to account for the fact that an advanced player might be tackling those quests and wouldn't need as much as the beginner player. The 1992 packs seem to have set it up for the advanced player but then not keyed the rewards for the beginner.
For instance... Potions of Healing are extremely valuable. Without these a character with no healing has in insurance against Death. You could say the Knight is a very powerful guy (but then so is the Barbarian and look what happens to him, not just because of the Yeti). He does have one healing ability but it's Stalwart, he just comes back with ONE body point. If you only give him the Healing 1d6's those can get unlucky rolls and he may just get 1 BP. Better to have +4's, +6's... anything else to help him not risk dying in each and every room (the monsters and wandering monsters in the '92 solo quests tended to be very powerful, like several boss level fights in a single quest at times). Traps are another thing... only the Rogue and Dwarf have the ability to disarm traps, so a starting hero will have no way to do that. Traps that trigger during story events, undetectable traps and traps on the other side of the door are already unavoidable (unless the behind the door traps are spear traps that could miss you via the dice).
The Knight, and I keep assuming the Knight would be the only choice for solo quests but that's not guaranteed is powerful yes, but many of his abilities have less utility in a solo format. His Shield Block only helps an ally, not himself. His Knight's Challenge would serve no function if there's no one else to re-direct a wandering monster (unless it's a rescue mission with an NPC). His ability to use plate without movement hindrance is nice but he doesn't start with anything but a shortsword and shield.
Besides healing potions, Equipment is more useful than gold, because it can immediately be put to use. Gold presumes you survive to the shopping phase between quests (similar to giving the equipment upgrades as rewards between quests).
If they make the quests for "any hero" then they have to contend with other issues like the fact that it might be the Elf picking a set of spells without healing, or it might be the Wizard with only his dagger to fight with. Would they cater to each heroic type? Especially if it's the Wizard playing solo, he's going to get most of his benefit from Artifacts, not found equipment.
Again, this should be an extremely easy thing for the "beginner" adventures. Once the basic hero (or heroes) are maxed out in terms of equipment and given a few potions, they're ready for the full difficulty quests.
The other "selling point" in 1992 for the Solo Quests is that it is a fun challenge when you "only have two players." The thing about HeroQuest up till that point is that all the quests were designed for 4 heroes (granted, there was at least one quest where two of the heroes were detained and had to be rescued by the other two) meaning two players would see one player controlling the four heroes and one taking the roll of Zargon. A solo hero has a much harder time because he can't use the door blocking technique, and he has to be self sufficient. If he dies it's over vs. having others to save you or at the very least scoop up your gear to prevent it being claimed by monsters if you don't make it. Monsters can target and pile on the attacks against a solo hero while the heroes can do the same back to the monsters in group quests. But a "solo" quest of one hero vs. Zargon also means turns will go faster because the good guy player doesn't have to manage all those extra assets (especially a spell caster, especially the Wizard). A group quest tends to take about 2+ hours while a solo quest might be finished in under and hour (with success!) if you stay on task.
It should be remembered that the EU fans got solo quests from Dave Morris' 2nd and 3rd HeroQuest novels in '92 and '93 as well but they were vastly easier than the NA counterparts. These were individual one-offs, not designed to get a "basic hero" up to snuff with a group on a harder group mission, but they each had an interesting approach... while the lone hero begins the mission he finds a companion who can help him out and complement his power.
Maybe they'll botch it up, but I think they have all the experience and tools they need already to make it a much smoother experience than American kids got in '92 (the few who actually played those packs back then). They also have the potential to overcome the "gotta catch 'em all" mentality that was being fostered by those themed hero packs from thirty years ago (the old plan was to get kids to buy all four of them to put them together and have all four heroes get all the possible perks... another marketing strategy like how HeroScape was designed to have you buy booster packs to buff out your army and build ever more elaborate battlefields... though savvy kids would have gotten together with their friends to bring it all together when they played instead of each one trying to collect everything).
If it's another broken pack, without the nostalgia holding it up, and negative reviews appear... it may hinder their future efforts, and it will just be hardcores like us who don't "mind" fixing stuff with our imaginations to keep it afloat. We're a portion of the market they seek, so it would be disappointing, as word of mouth would hurt sales and either it could mean the premature "death" of new HeroQuest content, or else if they can convince Hasbro to give them another chance, that they'd focus more on "safer" things like just remaking every last bit of legacy material and just keeping the popular sets on store shelves (even if that's just FLGS and virtual shelves for major retailers).
I'd rather see all the legacy stuff come out and quality original content than random "themed" sets everywhere like they have for Risk, Monopoly and Clue, wouldn't you? (though an anniversary re-creation of the Advanced Quest set would be pretty sweet, or a GWS collab for a true "Warhammer" aesthetic one even if it had to be limited is something a lot of fans would love to collect).