I don’t understand this one. If you pick a destination category when creating a draft it does remain set on the topic.
I thought about this (and internally it was suggested to just remove replies) but I have recently seen examples of cases where people create drafts that have multiple replies before publishing.
I think it is less surprising for it just to be a regular topic and let the editors work on it until it’s ready with the same tools and defaults as non-shared drafts. When it’s ready they can hit the button.