I don't think WAAS has anything to do with FANS. WAAS relates to GPS precision approaches, while FANS relates to enroute navigation capbility.
From what I know, FANS (Future Air Navigation System) includes GPS-updated FMSs, Datalink capability, ADS-B capability and CPDLC.
It is used over remote areas where radar coverage, and sometimes VHF communication is not available, for example airway L-888 over the Himalaya Mountains, across china.