Wenger does have free reign, he can do what he likes. And that is unprecedented in managerial terms, a manager is always vaguely answerable to someone. And know I don't think a manager coming in would like that, even managers like a structure....they will want to know they have the clubs support not the keys tossed at them "do what you like as long as we finish 4th".
That's not an atmosphere I believe any manager will want to join, the responsibility and authority Wenger has far exceeds anything Ferguson had at United, and it's a strong indicator of a leaderless club....a club that as long as the bottom line looks ok does not give a fuck about what is going on in the football sense and will take the same laisse faire approach to a new manager.
Unless there is both incentive and pressure to deliver, it's not an environment one can succeed in.