The ability to stack dis-similar 1/2 slabs in the same block. for example placing a cobblestone 1/2 slab in the bottom position and an oak 1/2 slab in the top position. To achieve this look now you would have to place the cobble in the top position and the oak in the bottom position of the block above it.
Would be interesting to see how a pick or axe wood interact with a block that is wood/stone. Would it first break the visual half being struck? ...OuO...
You would need to suggest this to mojang, but knowing how the code works, i can almost guarantee you it wouldn't happen.
