At one point Novartis had bylaws putting an eight year threshold for a top management tenure. (Vasella did overstep by one or two years) Maybe it has something to do with this move ? Not unhappy to see a MD coming back at the helm.
I always thought the duration was Jimenez's theory that a CEO should enter, rectify and then retire within a certain timeframe. I wasn't aware that it was a Novartis policy.