I use foundationless in all my boxes. In the honey supers, the bees always attach the wax on all four sides. While they don't attach the bottom of the wax in brood frames, I've never pulled out a honey frame when the honey is capped that it isn't attached on all four sides. I don't use an extractor, but if I did, I would have no hesitation putting a fully capped, fully attached honey frame into one....how's it any different from a frame on plastic foundation at that point?
Interestingly in foundationless brood frames, the bees often leave holes for passage between frames, something they can't do in plastic foundation.
Linda T in Atlanta