Let say all this is true, the leaks and the clues left by Grow and whatnot.
It is absolutely brilliant move by Microsoft. The first-party clause for making an NFL game has always existed, but nobody has ever wanted to get in the way of the 800 lb gorilla that is Madden (not to mention all the money Sony and MS make off of it regardless as platform holders). That said:
People will still buy Madden on XBO. By the millions every year.
Joe Montana is a perfect representative to start a NFL video game franchise around. John Madden hasn't been involved with the NFL in like a decade or longer since he retired from broadcasting. Millions of players don't even know what he did for the NFL or CBS and only know him as "the videogame guy". Joe Montana isn't a broadcaster or a studio/network guy, he's just a great representative of the sport to young and old alike.
I think EA would be pissed.
They definitely would lose some sales.