The 'system' concept is not new, but implementation is. Enough sats had to be put in place to make the coverage work, and even now, I dont believe the 88 have been launched.
Inmarsat has been marketing like crazy to get this service going.
A few things, the sat coverage, but the expense is what has really kept this from much wider usage, the airlines just dont want to pay for the service.
The position data sent thru the Ku band IFE systems has become much more popular, provides much more data, and is already costed in.
If there was ADSB-IN, then the aircraft could be a relay network in themselves....I think FR 24 is working on that.