Just a couple of ideas I had concerning the Sliding Block and its functionality.

New Blocks/Parts

Movement Pads: Arrow block. When a Sliding Block is pushed or falls onto one, it's pushed one tile in the direction of the block's arrow. Does not move players.
Heavy Switch: Sliding Block-specific switch. When a Sliding Block is pushed onto this 2-tall block, the top half will sink into the bottom half, like a piston, and the bottom half will emit a redstone signal once it's fully retracted. Resets when the block is removed.

New Mechanics
Smooth stone can be "etched" with a hammer and chisel to make channels to push a sliding block in, effectively constraining its movement to a track. These tracks can curve.
Sliding Blocks can contain a single stack of items, but said items can only be accessed via item-transfer mechanics (no direct inventory access)