Considering the limits of battery storage (in terms of Wh per kg, and Wh per cubic cm) and triple-junction GaAs PV cells. I question how useful a 1/4U cubesat can really be, if it needs to have both TT&C/bus management computer, some sort of Rx/TX radio to serve a purpose, possibly a single orientation gyro, some form of cold gas thruster for maneuvering, etc.

Even with a 6U size cubesat you are very limited in terms of data rate throughput (in Mbps) you can achieve in bands above VHF/UHF. Simply due to the size limits of antenna you can fold down and the Shannon-Hartley limit.