Kyle Rayner could be interesting,
John Stewart or Hal Jordan could be options, but what about Alan Scott from Earth 2 being a GL but what if that GL wasn't from the corps and it was like the Alan Scott from Pre-New 52, and is adapted in this universe. I don't know.
Anything could happen.
Remember in the first x-men movie most of the original ones were not shown and only some more were shown in later movies.
X-men first class was the origin of the x-men and most of the original x-men were not shown in that movie as well.
Darwin is a more recent superhero for example and he was shown over many of the older ones.
So whatever story needs to be told they could choose any superhero from the comics,past or recent or make up one for the movies or tv shows.
So it does not matter if the superhero is well known or not well known or new/recent.
So folks need to stop thinking everything will be like the comics,because it will not be the case.
Tv shows,cartoons,movies etc.. are thier own universes.
If they want firestorm or icon or vixen over aquaman,or show them first they will make it happen and the general audience will not have a problem with that for varied reasons.
Only some dc comic readers or hardcore aquaman fans will have the problem, just like when shazam became one the founders of the justice league war animated movie instead of aquaman.
Remember black widow in the avengers was shown first before black panther and the marvel version of hercules for example and hank(ant-man) may not be in any avengers upcoming movies.
Heck if the defenders superhero team have thier own big screen movie one day, marvel studios could have hank show up there instead if they want to.
Here is another example.
The defenders original superhero team will not be shown or shown as the founders for live action.