AMPV will replace M113.
However FFV at some point in the future, might end with family of heavy tracked vehicles.
GCV program intended to develop such family of vehicles, first variant was infantry fighting vehicle to replace M2 Bradley. Next would be self propelled howitzer to replace M109 Paladin, and later main battle tank to replace M1 Abrams, and if nececary other specialized variants like armored recovery vehicle, heavy assault brigde, armored breaching vehicle and so on.
But, FFV today have a low priority, high priorities to meet near term requirements is to:
Develop and field AMPV based on M2 Bradley hull to replace M113.
Develop and field ECP modernization for M1 Abrams.
Develop and field ECP modernization for M2 Bradley.
Develop and field ECP modernization for Stryker FoV.