Look it doesn't seem as though Lewis was a great offensive mind as a playcaller, which I'm convinced is Zorn's biggest issue after being a terrible motivator/leader. But here's the positiive things that could happen:
1) Zorn should be able to spend more time w/ the QBs and that's obviously his proven strength.
2) Lewis could "surprise" the defenses he faces w/ his play-calling, something Zorn has failed to do past week 8 of last season.
3) If Lewis has a stronger sense of the offens's strengths and weakness, from his birdseye view, he may be able to adjust the gameplan effectively. I don't believe Zorn has been able to even begin adjusting accordingly. It always seemed like Zorn drew up a gameplan, which may have been perfect if everything goes according to plan, but as things got off track there wasn't effective adjustments made. Result: predictability, lots of grinding plays that play right into the defensive strengths.
I almost want to feel hopeful the offense will rebound a little w/ this change...guess we'll all find out together