I know I'm in for a D&D story when there's a tavern (or similar) where a person in need offers a quest to the party. I could do with an expansion on what counts as a hip and happening adventure-hook establishment, but the underlying idea is fine. E.g., in my DW game, the main adventure-contract spot is Lady Safiyyah's Coffeehouse, because this is an Arabian Nights styled setting, and thus coffee houses are much more popular than taverns (though taverns also exist, mostly for the lower classes).
Honestly, despite the criticism it gets...I'd like to see MORE "Mos Eisley Cantina" stuff. Traditional D&D is medieval-Europe-inclined, but people often don't realize how much travel DID occur back then. Yes, the average villager might not have travelled much, but some, particularly mercenaries (aka D&D adventurers) and traders, often traveled quite widely. Marco Polo was far from the first person to do intercontinental travel, he just became famous for doing so. There were black Africans in ancient Rome, and they were known well-enough during Shakespeare's day that he didn't have to invent phrases for people to know what he meant when he called Othello a "Moor." Don Quixote features some Islamic (or at least formerly Islamic) characters. It's really not that weird to have some major hustle and bustle in terms of cultural interchange...in the big cities, in the places where trade and military skill matter.
So yeah. I'd like to see fresh life breathed into the "you meet in a tavern and a mysterious stranger gives you a quest," because it's Iconic D&D but a little staid now. And I'd like to see the Mos Eisley Cantina given the reasonable support that a pseudo-medieval setting could give it, if fans would let it.
Non-heroic adventures. Classic D&D seldom used "noble quests" as the motivation for PCs, often relying on self-interest or greed (treasure hunting). One of the best 1E adventures was Pharaoh, which starts with the player's exiled into the Desert of Desolation. The motivation was simply survival, but there was still a lot of story within. Most modern adventures seem to assume the party is noble/heroic, and not everyone wants to play that kind of PC.
Large scale isometric maps of the under-dark (OK maybe a bit niche but ever since the dungeoneer's survival guide I've loved these & yes I am in on the Survivalist's Guide to Spelunking Kickstarter)....
(All of these monsters are so foundational, they go back to Chainmail) Balrog Balor demon.
Roc. And not the Jungle Cruise one.
Meaningful md-tier undead (Wight, Ghoul, Wraith)
Stoners, dude. Basilisks and cockatrice.
Bags of Holding
Gauntlets of Ogre Power
Hiding in Shadows
Implausibly attractive women who try and betray the (male) protagonists
Lamp Oil flasks that are really Molotov Cocktails
Skeletons that were animated by some long-dead necromancer
All of the above remind me that it's a D&D adventure
I'd love to see more URBAN adventures. Especially at low level.