I suppose the advantage of bringing in another coach is that it doesn't disrupt any of what the other coaches are doing with their respective position groups. Goodwin obviously must have been successful with coaching offensive lines because he used it as a springboard to become an offensive coordinator. He coached for the Steelers, so I imagine he had something to do with a Super Bowl championship there. I have no idea if he has experience with the zone blocking scheme, or not, though.
Earlier this off-season, Zimmer gave consideration to Kevin Stefanski for the offensive coordinator's position, but opted instead to bring another coach into the organization. Perhaps he will do that again. He may be thinking that more great minds are better, especially for the offense, because that's outside of his personal expertise.
And this is not yet the final decision, so he may very well decide to make the changes internally, yet.
Alone we can do so little; together we can do so much. (Helen Keller)