I don't understand why so many of you think it is a good idea?
First of all, Rangnick would, barring a major and fundamental upheaval in the leadership of your club, not get the position and authority he is used to having and wants. Posters keep saying "hire him and then move him to DoF", well, you already have a DoF. Newly appointed. Who's going to fire that one to put Rangnick in his place? The guys who newly appointed him? Makes no sense.
Secondly, why do you believe his skillset is what's needed at Manchster United? You are not a third or fourth division club that can be made from scratch, with no history, or weight of expectation, or identity to frame the scope of his vision.
You don't need to be built from the ground up, using strict strategic measures like only buying U23 players with an internal salary cap of 3m per year (~50k per week), like he did at Leipzig. How is the situation at Man United in any way comparable? You have Pogba, Cavani, fecking Ronaldo, for christ's sake. You need a manager who can coach a team full of superstars and get them winning at the highest level. That's not Rangnick's specialty at all.
Connected to that is the fact that he's not even really been working as a manager, in the sense of coaching a team. He's done it at times, and when he's done it he indeed was pretty good at it. But still, the vast majority of his time in the last decade was spent in boardrooms instead of dressing rooms.
I get that many of you are yearning for fundamental change and some kind of methodical reform, but honestly Rangnick sounds more like a bad idea than a good one to me.