You're the only person I know from whom I could expect a knowledgeable answer to this question:
Listening to some Christmas carols, I get the impression that there was a time, perhaps several centuries ago, when certain modern musical conventions had not yet taken hold -- especially the division of time by powers of two. You know, groups of 4, 8, 16, 32 etc measures, each divided into full- , half-, quarter- , eighth- , sixteenth-notes etc. Certain carols -- "Foom foom foom"
[link] may be an example -- seem to ignore that convention, with charming effect, though it makes me a little dizzy to listen to them. Is this an echo of times past?