This is a suggestion for a change in behavior of mirroring. Many times, since I'm used to Rhino.. which I will argue is a much more efficient workflow when it comes to sketching, I will click what I want to mirror, issue the mirror command, then attempt to click the axis to mirror on. Each time, since it adds to what will be mirrored, I have to deselect the line or object, drag to the box press "select" on mirror line.. then re-select my line.
It would be way simpler, if the user has already selected an object or line, when entering the command, assume those are the objects/lines to be mirrored and already be ready to select the mirror line.
many other tools can use the same treatment as well.
