To answer another part of your question "are there technical constraints..", our research has mostly been inspired by practical challenges in micro and nano robotics. At such small scales, it is difficult (presently) to do onboard computation and these robots are generally controlled by a global field that is electric/magnetic/photonic/chemical gradient/gravitational etc.

The 'move without pushing' might require a state change (temperature dependent viscosity?). Perhaps we could use 3D robots that have shorter length scale in some direction than the others, and flip them sideways for flowing. Any suggestions?