Item Drop Buoyancy Differences

If a block of cobblestone was dropped in the water at the same time as, let's say, a feather, they would both sink and rise up to the surface of water at the same time. If you dropped these items together in real life, they would sink differently. The items act differently in the game, why not in dropped form.  This would not only provide a sense of realism, but could be used to make a non-stackable item sorter. Create a system to where you could time the items and sort them as such. Which also makes Sal tonight's big loser