As widely expected, it was announced today that Riccardo Chailly will become Music Director (Direttore musicale) of La Scala in January 2017, when Daniel Barenboim's original contract was due to expire.
However Barenboim will actually step down two years earlier, in January 2015, at which point Chailly will begin two years as Chief Conductor (Direttore principale). The difference in title reflects the fact that Barenboim has already laid out the framework for the 2015 and 2016 seasons, including the preliminary selection of repertoire and artists. Chailly's responsibilities for those two years will begin and end with the works he conducts. If you don't like La Scala's schedule, Chailly's temporary title suggests, blame Barenboim.
Chailly's current contract with the Gewandhaus Orchester Leipzig runs to 202o. There's no indication yet whether he still intends to fulfil it, but Barenboim has managed to combine the Staatsoper Berlin, the West-Eastern Divan Orchestra and a full solo career with his La Scala responsibilities.