Doing a little search on scansion, I find several other systems have been proposed in the past century, all of them moving away from the binary stressed/unstressed. Most of these waver between three and four stresses. American poet Alfred Corn proposes a three-stress system that merges the half-strong and the half-weak categories of Otto Jesperson’s four-stress system, devised in 1900, leaving strong, medium and weak stresses. Corn puts forth this argument in his 1997 The Poem’s Heartbeat. But Derek Attridge proposed a super-complex system in his 1995 study, Poetic Rhythm: An Introduction. Corn and Attridge need further study. Nabokov’s work on prosody also needs to be looked at, if for no other reason than he seems to have hated the idea of poetry and music sharing notation, or perhaps even the same aesthetic space.
One very interesting item is that Unicode characters have been devised for metrics. Unicode, a computing industry language for consistent representation of text found in most of the world’s languages with writing systems, include such things as Greek metrics: triseme, tetraseme, pentaseme. These ‘semes’ designate the length of a syllable’s sounding rather than its stress. For example, a pentaseme would be the length of five syllables, and the stresses within that length may shift. It could, I suppose, have a rising or falling stress. When I lived in Greece, most of my English-speaking friends had trouble understanding Greek because the stresses, or lack of them, made the language sound like one continuous flow. That was explained to me as a difference from most European languages, which would have a weak stress, that is to say, three levels of stress, whereas Greek had only two stresses. It was very difficult for us to hear the stresses in the language. Homophonic words, distinguishable only by stress, sounded the same to us.