It would be useful to be able to select and move multiple cards in the timeline view.
Off the top of my head there are 2 scenarios that I see this used for:
  1. You plan out the project in advance but its delayed for some reason (funding is late, took more time to put the team together, etc.). You need to move all the cards bit further in the future. Logical way to do it would be to select all cards and just move them all together.
Right now it is practically impossible to do this because a project can consist of thousands of cards, and you need to go 1 by 1 in order to move them around.
  1. One feature is late for a week. The next 15 features depend on it. Since the first one is late, all others need to be moved a week into the future as well. Currently there is no other way to do it but to go one by one and move them.