I would be extremely reluctant to install any capability that the FAA says it will require, but whose exact requirement is not down in black and white. They have a rather checkered past in creating panics which suddenly change, or go away.
Example: In the late 1980s, we were told we would all be required to go to mode S transpoonders, although no formal rule change had been made. King Radio took the bait, and certified a Mode-S transpoonder. The FAA changed its mind, and King was left with a design for which there was almost no demand.
Right now, today, I do not know exactly what the FAA is going to require. Neither, I think, do they.