> you could still subdivide zillions of little tasks into their own applications.

This is the approach Rust+Rayon are taking. Rust is in a good position to enable this because of language-level guarantees. Using "a lot of little, single-purpose" tasks means that each task has to own its memory; Unix of course enforces this separation, but this comes with some overhead. Language-level discipline can achieve much the same thing, more efficiently.