So, a few things:
1) The bar should be able to grow or shrink to indicate the size of the list.
2) It would be great to have a slimline version that looks like a rotated version of the < and > buttons, so that we can have scrollable frames.
As for features, Vol was very keen starting off with the scrollbar as an indicator, but we can implement drag-scrolling after that, and eventually we can also have them smooth-scroll. (probably simply as an animation thing, where it still "snaps" to an item when you release the scroll bar, but it does so in a way that seems more natural)