The Wells investigation never really looked into this very much, especially since Belichick wrote the foreword to the book Football Physics which discussed things such as properties and aerodynamics of a football.
Still, as Goodell said 'ignorance is not an excuse' when it came to Payton. Given that Belichick is a multi-time felon by sports standards, he should be given a 1-year suspension.
Remember, Brady has a player's union to keep the suspension in check, Belichick does not have a coach's union to do the same thing.
YR