Microdevice-based electrode assemblies and associated neurostimulation systems, devices and methods are disclosed. A system in accordance with a particular embodiment includes a microdevice positioned to send signals or fluids to the patient, and/or to receive signals or fluids from the patient. The microdevice can include a housing having an external surface, and a signal/fluid transmitter/receiver positioned within the housing and coupled to a terminal carried by the housing. The system can further include a patient-implantable, flexible support member attached to the external surface of the housing and carrying the housing. The system can still further include an interface carried by the support member and connected to the terminal, with the interface being positioned to direct signals or fluids into patient tissue, and/or receive signals or fluids from the patient tissue.