Here is some additional insight about your question:
1U payloads on 3 separate CubeSats acting as a data relay is a valid concept. We are not looking for CubeSat concepts, we're looking for CubeSat payload concepts. Therefore the concepts do not need to include capabilities that would typically be provided by a host satellite, only the mission payload capabilities and concept. The concept can describe how a constellation of payloads would perform, yet be demonstratable with fewer vehicles and within the shorter timeline.