Armies do have a size limit, no?
I suppose if they had a repeating queue that would break once the army reaches max, with might make it kinda pointless.
Keeping an army filled to a template could be cool, as could copy-pasting said templates on order. Might actually get me to use the army unit order feature at all as I tend to turn my factories on to a unit ratio and let them produce for the rest of the game.
Barring economic destruction that is.