The possibility of the Beornings being descended of Radagast... now, that's an interesting thought. I'm still too flu muddled to want to go digging out and digging through the HoME books to find the reference, but I believe that somewhere in it is the statement that the longer the Ainur remained in a specific hroa, and the more they followed the ways of the hroa -- eating, drinking, and especially reproducing -- the more they became bound to flesh and could not easily return to their original state, or shift to another shape. That was part of Melkor's problem, and it would also appear to be part of why Melian was never the same after she left her body when Thingol died. The Istari are something of an unusual situation, since the particular bodily state in which they existed in the Third Age was imposed on them as a condition of their mission, and were real bodies, not the self-incarnate bodies a Maia would make to appear to and interact with the Eruhini. I would expect that the effects of being in that kind of hroa would not be quite the same as the effects of being in a self-incarnate fana/hroa, and thus would have different limitations. Some, we know, were quite profound, specifically designed and intended to limit their powers so that they would not be tempted to dominate and force the wills of the Children by their own might revealed. But I suppose it might be possible that Radagast/Aiwendil (who was indeed a Maia of Yavanna) had found ways to use the abilities of changing shape and hue early on in their mission, was good at it, and thus got a reputation. If he, as a shape-shifter (also early on), wandering the woods and wilds as a bear, had met a human woman with whom he had... er... relations (as a human, not as a bear), they might have had a child to whom he was able to teach the way of shape-shifting. It often seems as if Tolkien felt that when mortals and immortals had offspring, they would, unless other grace was granted, be mortal rather than immortal. Elwing was not considered an immortal Elf, nor was Earendil until they were granted the grace to choose. I don't know that there's any specific statement as to whether or not Dior and his other children would have been counted as mortal or immortal. In any case, if the son of Aiwendil and Unnamed Mortal Woman had children with anorther mortal woman, and his son or daughter did, etc. the line would eventually become rather like the Dunedain in the Third Age, longer lived than other men, with certain unusual gifts (like Aragorn's healing), but mortal Men nonetheless. A scenario like this could also explain why Radagast fell away from his mission, became enamored of Middle-earth, and apparently dwindled to the point that his heart was there, and he lost the yearning to return to Valinor. By having a child, he tied himself to that physical, limited, mortal world, and there he would stay.
It's another thought, anyway.
