but I also wonder how the winglets affect the wing tip vortex - a critical factor in AAR on wing pods. Do they intensify the vortex into a smaller cross section, or weaken it over a bigger cross section? I am not a fluid aerodynamics person!
They significantly diminish the intensity of the tip-vortices by blocking airflow around the tip from lower to upper surface.
Dryden experimented with winglets on the KC-135 in the eighties. I don't think there was any adverse effect on AAR. I don't know, however, why they did not retrofit winglets to the KC-135 fleet.
When you refer to "active wings", do you mean "active ailerons"? Whatever, the A330 wing is the same as the A340, so already has underwing hardpoints where the outer engines would be mounted. There are very few modifications required to the wing.