Well, Sandy,
The way I interpreted the statement was that partner dancing is two-way communication in which both partners play an active roll in the physical 'conversation', rather than the leader being active while the follower is passive. Of course that might not be the intent of the original author, but for now it works for me.
There's probably more to the leading=following=leading concept than I've worked out so far. Some leaders are clearly doing something beyond just providing good lead, musicality, and floorcrafting. Just as others are doing something worse than leading badly.
As to following becoming leading....I take an active roll in floorcrafting. I'll not only signal, I'll change direction, speed, or even alter a pattern in order to avoid a collision. After all, I'm a live person who dances for fun and dislikes pain, not an inanimate object or even a well-programmed robot! Of course it's different with different leads. When dancing with a novice leader I filter as much 'static' out as possible so I can complete the patterns with some style. I'll also try to subtly 'shape' his movement to keep us out of trouble on the floor. Not a good long term practice plan for a permanent partner, but it works well for a social dance. Some leads are skilled enough that I go on 'cruise control' unless someone is on a collision course from behind. Good leads tell me they like knowing someone is watching their back; they can relax and do interesting patterns instead of being on 360 degree hyperalert.
Interestingly enough, only men with such terrible floorcrafting that I resort to backleading in self defense seem to object. Some leaders want complete control of their partner and are totally unwilling to alter course ESPECIALLY when cued by a follower. (Even to avoid a collision. I find them frightening to dance with.) Perhaps ultimately it's a state of mind; people bring more to the dance floor than their training. How they relate to others is ultimately how they will dance with them.
The other place I think following could morph into leading is in mood and artistic interpretation, which is individual.There's maybe less room in standard for a couple to differ in how they respond, but in Latin/Rhythm and especially American Smooth the leader 'speaks' but how the follower answers might change the 'conversation' entirely. I've played with a number of different moods and attitudes in any given dance when dancing with regular partners; it's fun to watch what comes back. Usually I'll play it 'straight' at first, especially with particularly timid or rigid leads. But sometimes.....someone new comes along, the lead is almost perfect...adjusted...perfect...there's this 'click' and within a few steps I've pulled out all the stops.
Then there's the feeling when dancing transcends patterns, steps, lead+follow+beat+floorcrafting, and 2 separate people unite to move instinctively with the music, each other, and the universe. In perfect....well....Harmony 