According to the
Watchtower Database, Bruce Timm and Co. wanted to use John Stewart as their Green Lantern as early as the pre-production period for
Superman: The Animated Series. Before S:TAS, the team thought they couldn't pull off something on the quality of the Fleischer cartoons, so they were toying with the idea of jumping from
Batman: The Animated Series straight into
Justice League or something like
Justice League. They weren't expecting to be able to use Batman in that version of the idea, since his rights were tied up at Fox. That's why this art exists:
Maybe DC mandated Kyle Rayner on S:TAS? Who knows.
More details in the video below--
More info on the Pre-Season 1 Justice League:
https://jl.popgeeks.com/001/001.htm