I'm still misunderstanding. Holding B gives you the unit dossier pop-up, holding A shows you this:
The slashes are squares he can move to and attack, the empty boxes are squares he can reach via ranged attack.
I guess it'd be nice if it showed the attack range while trying out movement options? I'm not sure, it might get messy, and I'd rather plan out what I'm going to do before I move. You can do this on friendly and enemy units.
I think it could be done. Either give us a button that highlights all "hostile" tiles while pressed or make it so that when you are moving a unit, red tiles would be places that are inside a enemy's attack range.