What Would A Fifth Royal Child Be?

So we know there is:

1. The Throne Warden

2. The High King/Queen

3. The Song Maiden/Master

4. The Lore Wain

I've heard theories of ALL the children after the third being Lore Wains, but I don't remember the books saying that🤔. Maybe I'm wrong. Some theories of mine:

1. Maybe they would be an Explorer and go beyond the Edges of the Maps to make maps of the places they've been.

2. A scientist? They document all the strange animals and plants in Aerwiar

3. A mathematician?😂 I know I'm clutching at straws here but it's just an idea.