Some of you people are not understanding the bigger picture here. Its not about a partnership or stamping "Nintendo" over the XB1 boxes, its about a mutual exchange. (hypothetically) MS wants Windows/live eco system to flourish, and this is where Nintendo is weak. On top of that, with M$'s vacancy, Nintendo inherits vast 3rd party support. 2 huge weaknesses now fixed for Ninty.
So M$ gets out of the way, basically in exchange for Nintendo Network *powered by Windows*.