Rangnick as DoF (so Fletcher and Marcel Bout working under him), Murtough above both him and the manager who is in charge of all football matters (including academy, first-team, women's club, relations with fans, etc), and then a CEO (likely Arnold) who is above him, with Joel/Avram at the top. I think this would be the best we can hope while Glazers are there.
In fact, this is not unseen in American sports, like NBA.
Coach and his assistants - coach the team (equivalent to the manager here)
GM - chooses the coach, deals with signing and trading players.
Director of Basketball Operations - above GM, in charge of all basketball things.
President - above Director of Basketball, pretty much in charge of everything.
Owner - hires and fires the President.
Of course, GM and Director of Basketball Operations often is the same person, but it does not need to be. Same as how the DoF could be a different person to Murtough, and report to him. I hope something like this happens, even if the official titles are different. For example, Rangnick can be called consultant for all I care, as long as he is (mostly) in charge of hiring the next manager and doing new signings. Murtough can be above him, although it might be a bit awkward considering that Rangnick is far more experinced and established, but as long as everyone is fine with it, seems a decent model.