Doesn’t Dorico already get close to this if you give a solo “player” (i.e. a generic singer) several “instruments” (i.e. different characters) and then switch off the messages like “change to Hamlet”?
If there are notes in more than one of the “instruments” you do get multiple staves in the score - but I don’t know whether that is by accident or design, in the current version of the code.