I really don't think Razer is going to become a Green Lantern. I think the reason the producers went with the lineup they did -- Hal, the much burlier Kilowog, the red-suited Razer, and the white-and-green Aya -- is because they're more visually diverse than a team of four GLs would've been. Color and design are important in animation for distinguishing characters, especially at a distance or in cluttered or active scenes, and it's weak design to have your main characters resemble each other too closely. (This is why The Real Ghostbusters
gave the four leads differently-colored jumpsuits and very distinct hair colors and styles instead of going with something closer to the movie cast. It's also probably a factor in why the main casts of Avatar: The Last Airbender
and The Legend of Korra
include representatives of multiple different nations, each in their own color-coded wardrobe.) Kilowog's distinct enough from Hal in size and shape that the similar colors and designs of their costumes aren't much of a problem, but Razer is much closer to Hal in build, so I don't think Timm would ever want to put Razer and Hal in the same color -- not as long as he's a member of the core team.
Anyway, I think the takeaway from "Blue Hope" is that rage is too fundamental a part of Razer's nature, that he's just intrinsically best-suited to the red ring -- but that he's finding a way to draw on righteous anger and wield the emotion constructively rather than giving into hate. I think a part of the whole emotional-spectrum idea is that none of the emotions are intrinsically bad; they all serve a purpose, but can be wielded positively or negatively. So giving Razer a different driving emotion than Hal and Kilowog makes the characters more diverse in personality as well as design, and that's not something it would be desirable to give up.