Do you know any song lyrics written in pentameter (iambic or otherwise)? I wonder if it would need to be in a 5/4 time signature...
I can't really think of any (followers, anything to recommend?) but it definitely wouldn't need to be in 5/4. Poetry kind of naturally has a pause between lines, which could (and, I think, should!) fill one or more musical beats if you were preserving the meter of the words in such a way that each foot is a musical beat.
(I don't know how much you'll get out of this if you're not a classics nerd, but some of Tyrtarion's musical settings of Latin elegy and epic demonstrate really well how the line break and optionally the caesura can be its own beat.)
Besides, there are other ways to preserve the meter, such as making each foot a measure (of 2/4 or 3/4). And of course music doesn't always follow the metrical structure of the words that are sung!
