Given that the power budget for a cubesat is unlikely to support a linear transponder in a meaningful way, an FM transponder would be nice, IF it includes a decent receiver. If the uplink is dependable but the signal weak, i think people will still use it. It won't be an 'easy sat' and folks will need a better receiving set up to use it (such as an 'Arrow' rather than some kind of omni). It should at least be a good experiment.
My suggestion is to have such a transponder available once the primary mission of the cubesat is complete. Thus, like DO-64, there is likely to be a lot of interest in receiving telemetry given that folks may be able to use the satellite themselves later. Like DO-64, having a machine- independent telemetry decoder makes it possible for lots of people to participate. Best of luck to you!
-- KD6PAG (Networking Old-Timer, Satellite QRPer)