Multiple mine / excavator priorities

Right now, it's possible in Update 1 to prioritize 1 mineral per excavator. While this is helpful, it would be even more helpful if it was possible to assign multiple priorities with a ranking system. For example, in the early game, it's critical to build up iron and copper reserves. There is a lot of dirt in the way of getting to those reserves. I'd like to tell my excavator to mine iron first, then if there are no exposed iron deposits, then go after dirt and then rock. Since there are some places where sand overlaps, I want to be able to tell the excavators not to load any sand. When sand is in the way, there ought to be a way to tell the excavators to move it out of the way.