The door animations of trains have different durations, so there should
be a W command to let the train wait until the doors are closed, just as
it happens with braking commands.
Certainly a good point, but would require a change. ATM, the "train" entity has no idea of the door state of the wagons. The control/atc command just sets a variable in the train, and every wagon checks and applies door animations individually. The same is true for the horn, which is why there's still no ATC command for this.