You are right that the data-value-update attribute is not yet documented. We will update the documentation to include this setting. We will also update the examples.
The data-bind attribute is meant only for binding purposes. Any configuration settings are set via separate data attributes.
Implementing afterkeydown is possible however requires a setTimeout because the value is not updated when the keydown event is raised. We would really like not to include such code because it is very hard to test and is a potential performance hit.
the Telerik team
Join us on our journey to create the world's most complete HTML 5 UI Framework - download Kendo UI