Yeah I agree. Part of the point of lean is not specifying too much too early. Inevitably new ideas, problems, priorities will crop up and if you've specced out too much too soon, some of it will go to waste.
Perhaps the ability to hook up with APIs would be useful though, so you can manage features and bugs in other tools (GetSatisfaction eg).
My #1 feature request would be to make it touch-screen enabled. Along with flexibility, the other major benefit of a physical storyboard is that it fosters communication and collaboration by forcing people to get up from their desks and talk face to face. Also in standup meetings it is invaluable to be able to stand around the board and talk about what it is showing you regarding blockages and flow, and immediately do something about it. So ideally you'd project the board up on a big screen or a big TV or something. Then if anyone has an ipad or iphone handy, you can update the board on the fly.
Perhaps the ability to hook up with APIs would be useful though, so you can manage features and bugs in other tools (GetSatisfaction eg).