I seem to recall "detached equipment" being called on a live ball that did NOT have a chance of going fair: it was a pitch not swung at.
The Dodgers were playing somebody or other, R2, outs don't matter, and F2 blocked a pitch in the dirt, while pulling his mask off. As the ball started to roll away from him on the 1B side, he used his mask to corral it.
I believe it was Eddie Rap. (doesn't really matter) at 3B who called detached equipment and awarded R2 third. The FOX announcers took a while to figure that one out.
Point is: the provision about "possibly becoming fair" would apply to a batted ball only, and detached equipment is possible in other situations.