Creator's Pest: Alex Ross famously dislikes Kyle Rayner, and goes out of his way to avoid drawing him.
Follow the Leader: Alan Scott began his series as an engineer, but by his third story he's going after a job in radio at Apex Broadcasting. Add feisty female reporter Irene Miller to the cast, note that Alan took the job so he can keep up with news and learn about crime more quickly, and suddenly it becomes very apparent that Green Lantern is copying the same formula as Superman in an attempt to be just as successful. Even Green Lantern's original powers involve the ring allowing him to fly and making him invulnerable to metals, much like Superman. Constructs made of energy are the exception, not the rule.
Science Marches On: Some color theorists have suggested cyan should be considered a color of the rainbow, in between green and blue. Whether they will ever make a Cyan Lantern Corps (and what emotion it will represent) is unknown.
Gerard Jones also had plans for an Emerald Dawn III and further appearances of John Stewart as a Guardian.
Ron Marz stated that he was in the process of bringing the Corps back near the end of his run, which would have seen the Corps rebooted into a smaller group led by John Stewart and Ganthet as the Guardians. Unfortunately his contract ran out, Judd Winick went another way and we had to wait till Rebirth to get a corps back.
Also by Marz was the Elseworlds Green Lantern: Camelot in which The ENTIRE cast of Green Lantern would have been transposed to the time of Camelot, with Alan Scott as King Arthur, Hal Jordan as Lancelot, and Ganthet as the Lady in the Lake (Marz: He has a dress!).
After losing his yellow Power Ring and after the Zero Hour crossover, then-current writer Beau Smith wanted to revamp Guy Gardner as an Indiana Jones-type hero (i.e. without his powers), but he was forced by editorial to add the Vuldarian shape-shifting powers. You can learn more here.
During the planning stages of Infinity, Inc., Jerry Ordway thought about including a teenage male Harlequin who was to be mainstream comics' first openly gay character. Because the team already had two GL-related characters (Jade and Obsidian), though, the idea was scrapped.
Larry Niven wrote "The Green Lantern Bible", which would have established the Post-Crisis history of the Green Lantern Corps. Some of the stuff would later appear in the 1992 one-shot "Ganthet's Tale" (co-written and drawn by John Byrne), and parts of the bible can be seen in his 1991 book, "Playgrounds of the Mind".
Green Lantern: Rebirth's original script was slightly different, most notably in having Batman be host to Parallax (which Executive Meddling overruled), but also stating that Sinestro would be an anarchist. This element was apparently abandoned internally, as Johns wrote Sinestro as a fascist going forward.
Johns' early issues of Green Lantern had Black Hand and Shark as characters revamped in-universe by Evil Star, an old Green Lantern enemy. A few issues later, a Blue Lantern mentions Evil Star menacing her homeworld. This storyline would be abandoned due to Blackest Night.
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