My thought on the subject, while I hate to see Sioux go, is to find a way to evolve elements of the current logo into the new. That said, I think the natural choice would be playing off of the feathers in the current logo and evolve that into a bird of some sort. Perhaps and eagle. Maybe researching the Sioux name for Eagle. I think there are ways to pay homage to the Sioux and keep it incorporated while changing it enough to staisfy the NCAA.
There is a story of Spotted Eagle and Black Crow that is kind of cool: http://pyramidmesa.com/wrsioux5.htm about a warrior being betrayed by a friend, left out on a ledge to die and was saved by eagles that helped him return to his tribe. In the end, he returns to the Eagles that saved him and fed them Bison meat and honor them.