For nearly all of Arrow’s run, John Diggle has been a intricate member of Team Arrow, essentially serving as Oliver’s second-in-command and moral compass. However, there have been frequent discussions among the fans about whether John should trade in his leather jacket and put on a costume and mask to fit in close with Oliver, Roy and Laurel, and some have suggested that he should become the Green Lantern, i.e. the “Flarrow” (Flash/Arrow) universe’s version of John Stewart. Now, the actor playing Diggle, David Ramsey, is saying that even the official Arrow people have talked about using the Emerald Knight on the show.
When asked by Comicbook.com whether he would be interested in becoming Green Lantern, Ramsey implied that there have been discussions among the top Arrow brass about exploring that possibility, although, as expected, it’s being kept vague. Said Ramsey:
But, I mean, I’ll say this: it is top secret. David Ramsey has asked them, and they’re like, 'we’re working on some stuff.' If that’s the case, it’s gonna be huge. This is the stuff they want to avoid. I think they don’t want anybody to know yet and they haven’t even told me. They have told me that they are thinking about it and they are considering it.
Although he’s being kept in the dark on these developments, Ramsey said he would be open to the idea of playing John Stewart, calling him an 'awesome character.' As the third Earth inhabitant to join the Green Lantern Corps, John Stewart has been an important figure in the Green Lantern mythos since his introduction in the early 1970s, and he experienced a surge in popularity when he was added as one of the main characters in the Justice League animated series.
The main obstacle of Diggle taking this path is that extraterrestrial elements have yet to be introduced on Arrow. However, given that The Flash has opened up superpowers to this world, there may be a way to introduce alien elements, especially if the CBS series Supergirl is established as taking place in the same universe. (Although they would have to explain why none of the people on Arrow or The Flash have ever mentioned Superman.)
The other problem is that in many ways John represents the everyman of Arrow. In a show full of masked vigilantes and colorful villains, he’s one of the few “normal” people among the main characters who’s out there taking on bad guys. No mask or strange weapons in hand, just a standard gun and his combat skills.
Putting on a costume or giving him a ring that runs on willpower takes away this key aspect, so if he were to become extraordinary, it would have to both work narratively and not change his character too drastically. And that could take several seasons, not necessarily happening within the next year or so. If his identity becoming too well known presents a problem for the team, they could just have him wear a ski mask out in the field. All this being said, having a Green Lantern on television is an intriguing idea, and if Hal Jordan is chosen as the main ring slinger for the DC Cinematic Universe, having a John Stewart-analogue on TV would make for some interesting stories. It already helps that both Diggle and Stewart have military backgrounds.
There is one thing that Arrow would be wise not to do: pulling the same trick The Dark Knight Rises did with John Blake and reveal that his name was something different this whole time. If John becomes a Green Lantern, fine, but don’t suddenly retcon it so his last name was really Stewart or that he had it changed to Diggle. John Diggle, Green Lantern of Sector 2814. That already has a nice ring to it.