i think the capsule should stay on the train until it meets the next station; where the empty capsule will be picked up and another full one slid on in its place from that station and the cycle continues. Then the distance between the stations can act as a buffer. This should only be used in express, non-stop, or anywhere where there is 1,2 or more hours between stations. that should be enough time. for additional speed the capsule can carry the luggage in containers that can be lowered in to the train. Anyways, no one said this system has to be used at every station, if there train route dose not meet the criteria stated above (AKA local trains, HSR commuting stopping patterns like in japan) then load them in the regular way.