There were plans to animate an impromptu wedding between Alicia and Welkin in the midst of battle atop the Edelweiss, with sketches of Alicia's thrown-together wedding dress. This was dropped due to time constraints.
The art book reveals that Darcsens were originally intended to be a race of cat people, and that the series in general would have much more fantastic elements, like the Empire possessing lizard cavalry and much greater prevalence of large superweapons. Edelweiss' original design looked more like the title tank Metal Slug.
Alicia's first name was suppose to be Alma.
An old base for Faldio had sleek, black hair and glasses, before his look was finalized. Rather than scrap the design entirely, it was folded into the creation of Mica. This could explain why he has a "main character" appearance.
Oscar and Emile Bielert were intended to be main characters who would join Alicia and Welkin the defense of "Border town" (probably an early version of Bruhl). There are even early design materials of them with more detailed sketches. This idea was recycled in the anime as having Oscar and Emile as part of Squad 7 even though they don't get much spotlight.
The anime has the following trivia:
Fan Nickname: Faldio is often referred to as 'Superman' for his ability to do no wrong at certain points in the anime. Probably to make his eventual fall that much more shocking.
Maximilian has been called 'Maxi-pad' by people who are familiar with the game, due to the fact that he seems to be a mama's boy and well, just look at Lelouch's profile.
Early on, the series itself was nicknamed 'Kana Goes To War' on account of Alicia's various goofy facial expressions.
Name's the Same: The new guy, Karl, shares a name with one of the squaddies. Perhaps they got around that by never referring to the name of the Gallian Karl.