The effectiveness of electric motors depends from the area of magnets surfaces. All motors I have seen have smooth working area.
I suggest make them ribbed. This ribs are parallel to the motion/rotation and considerably increase working area. The depth of ribs must be equal to the gap between magnets. In this case rotor and stator could be easily install into each other.
Increasing working area without general increasing the size of motor make it compact.
And increases momentum of force.