1x1 Compact piston block
At the moment there are two versions of Pistons the small block and large block both being only 2 blocks long. although it doesn't sound like much it can make a massive difference if there was a version of the piston that was only one block long, more compact piston builds could be made and to balance them you could always just have it go as half as far as a normal piston could.
And if we're following with piston improvements could you add a small block large conveyor version of the piston for small ships? Because not everything can travel through small conveyers.