A control which allowed for flexible timelines would be very useful. While you currently provide the scheduler, it is very geared and oriented purely towards "calendar" style applications.
A more flexible timeline control, which could use numeric entries and provide a linear display of multiple data items, would be incredibly useful. This would allow many powerful scenarios, including things like health reporting (ie: the MS help guidance at http://www.mscui.net/Components/Timeline.aspx), animation control (ie: Adobe Premier or ULead style timeline editing), event management reporting, etc.
The key features required would be the ability to specify the "time axis" -whether as time or a numerical quantity. From there, it would be having tracked items (ie: a row) as well as marker points or ranges. Markers could allow display (or edit) of specific points in time/events. Ranges could allow start/end sequences to be displayed or edited. Marker/Range picking capabilities would open up the ability to allow interactive timeline editing, as well.
As for my personal use case - we're planning to migrate our current legacy software's animation controls to WPF, and this would allow us to provide a much cleaner, nicer interface than what we currently do. By having a clean timeline, we'd be able to easily build an editor for flexible animation controls of just about any data. Our current plan was to build this on top of charting (as a timeline can somewhat be thought of as a "stack" of 1D charts), which I believe would work, but would potentially be a bit trickier than if there was a clean timeline control built-in.