Stacking different slabs

If this is added, this will open to many building opportunities and techniques :D Example, if we stack a cobblestone slab on top of a wooden slab, the cobblestone could act as the roof outside. If you go inside the house and look up, it would be the wooden slabs! This can also save building time and resources too!! Any slabs should be allowed to get stacked together regardless of what texture it is!!