I wonder if part of the problem is that people reading out loud have to concentrate on what they're reading in the immediate moment, and aren't able to look ahead to see where the sentence is going

This is one of the reasons music theory entered into it for me. When reading music, one of the essential skills is being able to read ahead. Punctuation addresses dynamics in terms of emphasis and intonation to a degree, but not in the same way that musical dynamics do. The reader must infer the general tone and delivery from the overall mood and emotion running through the piece.

In prose, one has the luxury of exposition, for example

"hello!" he said brightly

vs.

"hello!" he said nervously

both indicate an increase in volume, the the quality is different which would affect how the sonics work in a piece. But in poetry, there's no real indication at first glance. The title can help, but only a bit. By contrast, in a performance, the audience can see the performer's body language, face and hear the performer's voice and so has a lot of information from which to draw context.

The problem with this, to me, is that the writer is then part of the focus rather than the words, the ideas and the line breaks. This is a particular problem because I really think that part of enjoying and experiencing poetry is the work that the reader has to do to get inside the experience that the writer has built and then stepped away from. For example, motorcycles are built for consumers to ride, not to be given rides on. The difference is, it's easy to get on a motorcycle and figure out how it works, which is not something I'm convinced is true for casual readers of poetry.

So essentially, I'm struggling with how to convey the sonic qualities of poetry while maintaining the visual elements like lines/breaks and shape while ensuring that I'm doing everything I can to set the reader up to engage with the poem as easily as possible.

I certainly think that emoticons are a step toward a more comprehensive visual notation, but I'm curious to see what emoticons will develop into.