What I would like is the same (with some adaptations of course, like removing spellcasting, obviously, and adding a fire "single round command" on the topmost list) orders screen for units as the one for commanders.
It will use already existing implemented UI/mechanics, and alleviate a lot of problems commonly mentioned.
It will help against firendly fire (you could script your bow troops to fire-fire-fire then hide behind other troops). It will give value and flexibility to dual weapon types troops (light infantry/cavalry/poison spitters), with orders like hold-hold-fire-fire then attack closest.
It will also help "coordinate" flankers (very fast and flying units attacking without support even with hold and attacks) with slower units. Exemple : your huscarls could be set to attack closest, your vans could be hold-hold-attack rearmost, and your valkyries could be set to hold-hold-hold-hold-attack rearmost (just examples, not sure how it would work out in reality
).