I'm fairly ignorant about motor design, but my immediate thought was "isn't this going to exert pulling forces on the PCB traces?". Seems like that would limit how much torque your motor can exert? Which I guess isn't necessarily a problem for many applications.
The forces are pretty much shear forces in the plane of the PCB, which traces can handle reasonably well. Also, the amount of force per trace is very small - the motor only has significant torque because there are many traces per PCB multiplied by many PCBs.