Why a Duck/Via duct?
The trapping of the quasi military protocol, along with social graces of civilized society do indeed get tangled in the wonderful world of Martial Arts and Aikido.
If just shouldn't matter if the more senior or less senior practitioners of Aikido are in the first line or the last. What is important is understanding that your obligation to acknowledge those who have come before you and those who come after you is from the sincerity of your heart and not the ego in your head.
Our ceremony of bowing in, practice, and bowing out is not some game of military protocol, even though it is derived from it, but the individuals search for finding a gentle way to deal with the emotional turmoil and physical violence of life that causes disharmony in the self.
If by awarding colored belts you think to create harmony, that is the harmony of your mind, not mine. I tend to see the struggle of each person, even if my intuition tells me to not like, or avoid a person, I try to see the equality of all students of aikido, both new and very old, more experience students who have become teachers.
Our EQUALITY may not be so apparent as line up in some dojo's, but nonetheless, we all struggle to find mastery of our practice in Aikido which becomes an ever widening field of vision as we progress in days, months, and years. I am a student of having all people play the game no matter their ability. Maybe because it is the fun of playing, such as Aikido practice, that makes it more than a game, and less than a pitched battle of war?
Indeed, we are playing at being warriors.
Indeed, we are not seeking to become warriors, at least most of us are not, for we do not seek the means to kill as most warriors do.
Still ... with the harmony of our practice, it is expected to show as much humility, patience, and respect as we would have others show to us.
So, by this measure ... it might be thoughtful to not line up by rank and experience now and then, just as it might thoughtful for those who do not to line up by rank and experience now and then.
If you only know how to do things one way, how will you ever know another way?
Maybe, but to see what is in the world, sometimes you have step outside your door, not just look thru the window.