Isn't the technical difference between Schedueld and Charter the way tickets are sold. I.e. A schedueld airline sells seats directly to customers (perhaps via travel agents) but at the end of the day your contract is with said airline.
Charter airlines are not allowed to sell seats direct. They sell seats to tour operators who then market them, so your contract is with a tour operator (even on seat only deals.)
Thats was my understanding, correct me if I'm wrong. Therefore, lo-cost services always have been, and will be schedueld services.