Each baddie could easily be disposed of in a chain of adventures, ultimately culminating in the potential “rebirth” of these so-called Ghosts.
Eight episodes, all written by 6 Underground writers Paul Wernick and Rhett Reese, would be a simple, but exciting fix that completes the story with proper resolution.
As such, Netflix has another option on the table, should it want to wrap the story in an efficient, but thorough way: it could turn it into a limited series.