5e tried a Basic D&D. Four races, four classes with one subclass. No feats, no multiclassing. Limited spells and magic items. It was on par with what BX offered. Obviously, it was treated as a sampler and not a complete game.
The thing is, I don't know how you simplify 5e further without forking development. Likewise, you can add all sorts of advanced options to use, but if no additional supplements use them, they don't gain enough traction. You can put three different rule books with simple, advanced, middle versions of the rules, but the real version is the one compatible with the supplements and modules.