I decided to try and start some flags for other notable groups in the story. The Order of the Aquiline Cross features a "red cross in a ring of feathers." I decided to replace the ring with arched wings, symbols of the Stormchaser, flanking the cross in the center. There's almost no way to include a cross without it looking explicitly Christian in nature, but admittedly that isn't a terrible analogy to the group, given both their violent crusading history, AND their newfound, much more idealistic purpose.
...not to mention the business about eternal life....
In any case: Beautiful! I think I prefer the second one, although the first one looks less Christian.
Also, a flag for Clan Millorn that I had to do once I came up with imagery for a group of adventuring gnomes and halflings...
A flag for a bunch of grave robbers?

As for others -- how about the flags of Innenotdar and Taranesti? Not much more than historical value at this point in the game world's timeline, but potentially interesting nonetheless.