Returning to the matter of rhyming (and assonance, alliteration &c), in one of his Commonplace Books - I think the First, kept when he was in his early twenties - Burns considers this and, as far as I recall, wonders whether "some poet with a particularly nice ear might make a song which dispensed with rhyme entirely". I think the phrase "sameness of jingle" occurs, too; perhaps someone with access to a published copy could give the passage more accurately?