Madara called Kabuto a "madman" when he showed him the 6th coffin, so that doesn't sound like Mito, so you have to explain that as she was just a Jinchuuriki and there's plenty of IWR jinchuurikis.
She wasn't brought up randomly in the story either, rather it was quite deliberate. She was a Kyuubi Jinchuuriki that could sense hostility, hence his rationale; thus, he banked a strategy together that Naruto as host to the Kyuubi would have a similar ability that only that host would have and no sensor ninja would have, forcing the alliance the bring Naruto out. His plan worked perfectly.
I doubt she really knows anything critical about current Madara except possibly through Hashirama as they weren't on good terms and Hashirama did the fighting, not her. Besides, the Madara then is not anything like the Madara now it seems. He has Hashirama's DNA, the Rinnegan, Gedo Mazo, 7 Bijou, perfect Izanagi, the six paths of Pain, the amber pot, Zetsus, and the space-time may be new, among many other things. Madara was then just a man, now he has become more through all his acquisitions and planning for so long. Thus, even if she had info, it's well outdated and not much use. It was an interesting post by someone forget who in my recent thread, but it's highly unlikely to me.
I simply see no elite value for the 6th coffin nor why resurrecting her would be madness, she was just an Uzumaki Jinchuuriki who knows a good deal of Fuuinjutsu. Thus, she might make a nice Edo Tensei but falls short in the 6th coffin category to me, but that's just my opinion.
Peace
