Metre: The End of the Line

I'm in the middle of an old-fashioned exchange of letters (envelopes, stamps, mailboxes, everything but the pony express) with an old friend about poetic and musical metres. (It's a fascinating, if often confusing field, not least because poets and musicians tend to count things — metre, feet, stress, accent etc. — slightly differently (in particular, as a musician, I think I recognize an anacrusis — a pick-up —  more readily than most poets do. (Entertainingly fictionalized, and in his usual obsessive style, Nicholson Baker's novel The Anthologist treats this question.)))

I think we have reached some consensus that song and dance metres differ from each other in a fundamental way in that dance assumes, indeed requires (i.a. so that dancers don't fall over themselves trying to follow a stretch of music when a foot/beat too many or too few appears or doesn't) a continuity from measure to measure, a non-stop flight of music (the music always goes on, and sometimes its vamps to allow a dancer to come in on the next rhythmic cycle when one is missed), while the line-to-line continuity of poem and song often has got to be more flexible. A voice has to breath, after all, and the listener probably needs some time to catch the sense of the text.  So how is this flexibility realized in performance?  Will a series of, say, pentameter lines, admit either regular or occasional additions of a foot or two, whether for breath or sense or just a break in the texture, becoming hexameters or longer, or should the measure vamp (whether imagined or via some form of acoustical accompaniment) allowing the reader/reciter/singer wait for the next line to jump in?  (This happens a lot in South Indian music.)  Or do these insertions of time intervals at the ends of lines exist in some kind of "zero time" as in some of Christian Wolff's cuing pieces, a break in the continuity that literally "doesn't count"?  And what about texts which contain sentences that wrap themselves around the end of a line, ending somewhere in the middle of the next? (This is actually surprisingly rare in premodern verse/song.)