There are some ideas on the reddit rejected and fps lists that I would like to see...
Automatic crafting, block placing, block breaking, villager trading.
Doors, trapdoors, bars, and chains in gold and copper. More orientations for bars and chains and glass panes.
Vertical slabs and stairs. Concrete slabs and stairs.
A lamp whose brightness equals it's Redstone signal strength and a sensor whose Redstone signal strength equals the block light level.