The important figure is of course the number of qualifying airframes and the length of time each of those qualifying airframes are airborne outside of line-of-sight of VHF/VDL receivers. So if only airframes capable of carrying more than say 30 pax that were outside line-of-sight of VDL receivers were included the required bandwidth would be a lot less. This is still possibly too expensive with the current bandwidths and comms, but I suspect that within a few years that will no longer be the case as bandwidths and capacity are increasing all the time.
A more difficult engineering issue is how to maintain a satcom link from an aircraft that has electrics problems or is in unusual positions due to loss of control. Those requirements would seem to rule out use of geostationary satellites and indicate what would be needed would be a connection oriented 'always on' link with low power requirements with one or more omnidirectional antennae on the aircraft.