It would be great to be able to create contact source folders via the API like we can when using the ScheduleMailing API call with the CREATE_PARENT_FOLDER parameter. We can already define where a contact source should be stored but that folder must already exist. 3 specific API calls that could use this functionality:

importList

createQuery

saveMailing

CreateContactList already supports this for contact sources and ScheduleMailing supports this for Mailings.