Being able to toggle auto-repair on buildings would indeed be nice, when I play skirmish half of my time is spent clicking on my buildings to get them fixed, and it is a massive chore.
How would that work? You have a menu item, click it, and as long as it is enabled, your buildings would start repairing if damaged? Or like a keyboard command that you use to start repairing all buildings that are damaged at that point in time?