There is only two ways this works: Explicitly marry D&D to a single setting and explore that setting in enough detail to go over multiple regional differences, or remove any sort of flavor text in the core rules and force the purchase of setting books to understand how anything it put together. I don't see either of those options being popular.
The first example would require D&D to adopt a Golarion-like approach a single world (and lets face it, it will probably be Forgotten Realms) where we no longer talk just about high elves and wood elves in the general, generic sense but of the elves of Silverymoon, Evereska, the High Forest, Evermeet, Yuirwood, the Forest of Amtar, Mezzobarrazan, etc. Lather-rinse-repeat this for orcs, dwarves, halflings, gnomes, goblins, dragonborn, tieflings, etc. Its certainly doable (many RPGs focus on a specific setting with distinct cultures per region, Pathfinder again a great example) but this focus will come at the expense of every other setting, since I don't think WotC could handle this kind of focus for every setting in the multiverse. Settings like Eberron, Greyhawk, Ravenloft, Dragonlance and Dark Sun (not to mention newcomers like Ravnica, Exandria and Theros) would be sacrificed to keep this sort of nuance possible.
Alternatively, I guess you could put a generic elf, dwarf, orc, etc in the PHB with a picture, a physical description, and maybe a few words on personality (elves are graceful, dwarves and tough, orcs are aggressive) and leave ALL the flavor text to setting supplements, but that seems to be unsatisfactory as well. Newer DMs won't necessarily know how to create these unique cultures, so you are raising the price of the starting package to PHB/DMG/MM/Setting, and that brings the cost to start in the game to $200 (assuming the current $50/book pricing).