I'd like to see campaigns move into a more epic level too. Acts III/IV (or beyond), with much harder monsters, bigger maps with tougher objectives, and 'uber' powers for the heroes. The 'Epic Level' stuff like they did for Warhammer Fantasy Roleplay. I really enjoyed our Gold level campaign in RtL where the heroes were nails, and the monsters couldn't be underestimated either.
And an aside from this, I'd like a bit for 'city' detail. I'd even go as far to say city map sections wouldn't go amiss. I can see them being used a fair bit in the story driven campaign. I know it's 'Journeys in the Dark', but there's only so much 'in the dark' they can add before they need to come out the other side
Or maybe they need an underworld theme at some point… They dug too far I jest
The tiers of campaign are a good idea I think, kind of like how WoTC pushes out the adventure series for Heroic/Paragon/Epic tiers of heroes, I could see FFG doing a similar thing in Descent. You could even look at the base set campaign as mostly "Heroic" tier with some lead in to the next tier if you use the WoTC examples of adventures:
Heroic: The fate of a village might hang on the success or failure of heroic tier adventurers, to say nothing of the characters’ own lives. Heroic characters navigate dangerous terrain and explore haunted crypts, where they can expect to fight savage orcs, ferocious wolves, giant spiders, evil cultists, bloodthirsty ghouls, and shadarkai assassins. If they face a dragon, it’s a young one that might still be searching for a lair and has not yet found its place in the world—in other words, much like themselves.
Paragon: The fate of a nation or even the world might depend on momentous quests that such characters undertake. Paragon-level adventurers explore uncharted regions and delve long-forgotten dungeons, where they confront savage giants, ferocious hydras, fearless golems, evil yuan-ti, bloodthirsty vampires, crafty mind flayers, and drow assassins. They might face a powerful adult dragon that has established a lair and a role in the world.
Epic: Epic adventures have far-reaching consequences, possibly determining the fate of millions—in the natural world and even places beyond. Epic characters traverse otherworldly realms and explore never-before-seen caverns of wonder, where they fight savage balor demons, abominations such as the ferocious tarrasque, mind flayer masterminds, terrible archdevils, bloodthirsty lich archmages, and even the gods themselves. The dragons they encounter are ancient wyrms of truly earth-shaking power, whose sleep troubles kingdoms and whose waking threatens existence.
As far as alternate tiles, I would buy those in a heartbeat for homebrewing, even faster if they came with extra quests either standalone or campaign alternates!