Linear Motors and/or Rails
It would be great if we has a set of blocks that acted like a linear motor, i.e. a motor that travels in a straight line flowing a track.
Basically this would require two blocks a motor which would connect to the sub-grid and a track piece which the motor piece would connect too and travel along with track pieces able to be placed next to each other to allow infinite lengths of track for the motor to follow, It could then be expanded with different type of track piece to make it even better such as station piece which act as select-able stopping points, and maybe corner/junction blocks to allow a change in direction of the motor.
These blocks I feel would be great for building elevators (from small personnel, to massive ship lifting ones), trains & very large sliding doors. The near infinite range of movement make them different from pistons, but unlike pistons they do not themselves act as conveyors.