To have a HeaderCreated option for the RadScheduler to allow you to customise the header in timeline view.
The HeaderTemplate can be created for all views, not only the Timeline view. That would allow users to have the same custom controls in all views.
As the free space in the header element is quite limited, the controls added should not be too big to distort the header's appearance.
For bigger and numerous controls, a better option would be having them outside the Scheduler, which is also the current possible approach for the Scheduler.