Just to add to this - I’ve just come across a very good use case for being able to select currency for draft orders.
As you might be aware, if a customer pays for a normal frontend order in a different currency to the store’s default, the order cannot be edited.
My first thought was “fine. we can just cancel the order and create a new draft order for the customer to accept”. Well… turns out that’s also impossible. So that’s the use case!