Boeing has been awarded a patent for a new winglet design. See below for a quick look.
Notice the device has the traditional upward sweep. But look below the wing at the loop. This loop may be hollow to allow air to pass through. As the link shows, Boeing claims the loop may have various shapes; triangle, rounded, parabolic, semi circular and trapezoidal.
The document includes this detailed view of the winglet.
This may give us some idea where Boeing goes next with its ongoing wing work. For its aircraft that have the swept back wingtips this does not look like a ft. But to keep the 737 design current in the hyper competitive single aisle market, this could do the trick. How much this design improves on the winglets of today is not clear – yet.