The 767 (and 757) winglets have all been STCs by an outside company (I understand Boeing has been 'helpful' with drawings and technical information, but not directly involved in the design or modification. I have a buddy that works for the company that did the 767 winglet STC and I've not heard any indication that they plan to do a 'split scimitar' configuration for the 767 (or 757) - but I haven't talked to him for a while.