This is exactly my use case! (Only for a musical, but it’s the same idea)
I’ve been using “one player with multiple instruments” to model different characters, as as mentioned, changing the character usually shouldn’t create a new system. The change is usually written simply as the character name.
This generally works well to automatically switch the character mid-system:
, and also automatically use multiple staves when needed.
But there are a couple of problems with that approach (edit: I’ve realized that should probably be a different topic, so I opened one here: Handle characters/roles in a vocal piece better (feature request))