If you've ever spectrum analyzed c-band and if you can get Telesat, SES and Intelsat to come to a transponder loading arrangement, I think there are 4 transponders per satellite to spare for now as there is such a c-band frequency surplus.
With technological advances, the amount of c-band bandwidth likely could effectively increase in the future if there is ever a need. For instance in the past, going from VC2+ analog to HD digital, what used to take four SD VC2+ 36-mhz wide transponders can be done in HD using only a quarter-transponder or a half-transponder. Nowdays, advances are like more efficient video compression, modulation and rolloffs that allow for more in less transponder space.
