If the NFL isn't going to suspend anyone because they can't put it on anyone specific, a new policy will be announced very soon. Balls will be checked during games.
I honestly have no idea how they can pin it on Belichick unless he was spotted handing someone a shoebox full of cash with handwritten instructions to deflate the ball. The balls are checked, by NFL reps, two hours before the game. Unless they expect the coach to carry the balls around for the next two hours, and keep a watchful eye on them during the game, it's pretty much out of his hands. As I jokingly said, RGIII would deflate balls during the game and report it in order to get Gruden suspended. Some crazyass ballboy could do it out of spite.