I would like the addition of two new hairpin line shapes. The first would be a crescendo followed by a diminuendo. The second would be a diminuendo followed by a crescendo, each of these shapes combined into a single line.
These new lines would provide a quick and simple way to create a hairpin up followed by a hairpin down or hairpin down followed by a hairpin up where it is required that these appear on a single note. (called messa di voce in singing).