Around here FAST is the legacy term and RIT is the current term, being encouraged at NIMS and basic firefighter and RIT classes. But also, around here, everybody who might participate or need their services knows they are synonymous, and there is most definitely a move to adopt RIT.
It'll be years before the transition is close enough to complete, and years more before others like "tanker task force" are changed to "tender strike team". Does that mean it is not worth doing? I disagree, my personal opinion that standardized terminology for interoperations purposes is a worthy goal. (Standardized communications, as in radio frequencies and technical compatibilities, is a related but separate issue.)
Jim