I know I'm probably going to get blasted by the hard core fans but here me out. We know Klaus's father and his people were already present when Mikael and Esther arrived in the new world whose to say that Klaus's father's pack weren't allied with Native Americans? Also the witches and werewolves go around acting like they deserve the Quarter but we don't really know who the true owners of the land known as the french quarter were.
That being said a group of native americans likely skin walkers could come to the French Quarter seeking retribution against not only the wolves but also the witches and if they had ties to Klaus's father maybe they could also be like his lost siblings assuming skin walkers could live for long periods of time. If that were the case I could see them coming to NO to kill Mikael out of revenge.
I like this idea because skin walkers are like a witch and werewolf combined except they arent just limited to one animal form. That alone would make them formidable against NO witches.