I don't think that's possible.
I can't imagine any system that would (for example) run adventures in Middle Earth, Westros, Faerun, Night City, Gotham and Tattooine. If it did, they would have to be so plain and generic as to be "let's pretend, but with a resolution mechanic". Something like the Cypher system rather than D&D.
I totally disagree. Homebrewers have hacked 5e to fix a huge number of settings. All it require it for the core game to come with options built in. The game might have 15-ish classes, but with the assumption that only 4-12 will be used in any given game where they fit the milieu. Different magic-using classes would have different magic systems that fit different settings; Sub-classes could be built with different fantasy genres in mind (spellcasting would become a ranger sub-class, for example). Again, not every sub-class would be available in every game.
Middle Earth: Druid; Fighter, Noble, Ranger, Wizard; low-magic module; slow recovery; tradition fantasy spell list module; traditional fantasy races only
Hyboria: Barbarian, Cultist, Fighter, Noble, Ranger, Rogue, Warlock; low-magic module; all human PCs
Vancian Dying Earth: Fighter, Noble, Rogue, Magician (uses a real Vancian magic system); all human PCs
Westros: Barbarian, Cultist, Fighter, Noble, Ranger, Rogue; low-magic module; slow-recovery module; tradition fantasy spell list module; all human PCs
1e Faerun: Barbarian, Bard, Cleric, Druid, Fighter, Monk, Paladin, Ranger, Rogue, Wizard
3e Eberron: Artificer, Bard, Cleric, Druid, Fighter, Monk, Paladin, Ranger, Rogue, Sorcerer, Wizard
Age of Sail Historical Fantasy: Fighter, Noble, Ranger, Rogue; no magic module; slow-recovery module; firearms module; all human PCs
Early 1900s CoC-type setting: Cultist, Fighter, Rogue, Warlock, low magic module; firearms module; slow-recovery module; all human PCs
Tatooine: Fighter, Monk, Noble, Ranger, Rogue; Psionic feats allowed; high tech weapons module; space flight module
I absolutely believe this could be accomplished in two 350-page books by 1) moving all detailed rules explanations to the DMG and 2) cutting the abstract stuff nobody reads from the DMG.