This isn't possible, neither in 1.1 nor in 2.0. A train will only leave station, if it has a destination. In 2.0, you use interrupts for dynamically choose a destination. Whenever a train is about to leave a station, all interrupts in its schedule are checked, and the first interrupt with matching interrupt conditions is executed (its schedule is copied as temporary entries into the main schedule). So you cannot decide mid-route, but you can decide when the train is about to start driving. A common default destination if nothing else matches is a depot, by the way.