Chad thinks the game cerebrally about as well as any QB we've had since Don't Strock. His problem was always one of not having the tools to make certain throws reliably. He lacked arm strength to throw the deep out to the wide side of the field, or the bomb without winding up and putting a lot of air under the ball. So, he checked down a lot when those throws weren't wide open.
He could easily call/teach a far more aggressive game for a strong armed QB with a quick release like Tannehill. Remember, we run a variant of the WCO, which Bill Walsh designed in Cincinnati specifically for a weak armed QB, and improved it in San Francisco for a QB with a less than stellar arm.
Pennington's short passing style suits the WCO, and he would likely feel very comfortable in it.
I'd love to see Pennington pursue coaching. But, like everyone else, he needs experience before he merits an NFL assistant coach position.