Winglets may have been banned for 2017, but the drive for aerodynamics development continues. This time, however, winglet development will continue on the inside of the fairing, rather than the outside. The development ban applies solely to the exterior surface of the fairing, and not the interior.
What this means in practice is that while the shape of the fairing must be homologated at Qatar, with one update allowed during the season, that only applies to the outer surface of the ducts, and not to the vanes (the small struts or winglets inside the ducts which control the airflow and can be used to alter downforce) inside those ducts.
Development of aerodynamic control surfaces will still be allowed, as long as the changes remain on the inside of the fairing.