The ‘streaming instability (SI) is one of the leading mechanisms for planetesimal formation. Under appropriate conditions, the SI can drive the rapid growth of dust enhancements to the point of gravitational collapse. However, the efficiency of the SI under more realistic conditions expected in protoplanetary disks has not been tested. To this end, I present extended models of the classic SI, including turbulence, stratification, and magnetically-induced accretion flows. I describe new challenges and pathways for planetesimal formation via the SI when these effects are considered.