The concept is simple, but I don't know how feasible the implementation would be, but I thought it couldn't hurt to ask.

You've already got encased shafts, so you can pass mechanical power through a solid block. This is much the same but for piston extension poles needing room behind the contraption to appropriately retract. These would function as empty space for the pole to retract into, with a hole in the middle, but would also count as a solid block for purposes of building or walking. Effectively concealing the pole within!

This would make certain builds much cleaner, more aesthetic, and less prone to disruption from outside forces.

Thanks for your suggestion, it has been added to our public submission sheet.