I'm marking this as a blocker for 12. I believe that for the Sakai 12 release the gradebook tool as well as the dashboard (excepting possibly the entities DashboardEntityInfo and RepeatingEventGenerator interfaces) should be moved out of core and into sakaicontrib. The entity interfaces and impls would be relocated to more appropriate directories.
These are no longer being actively developed and there are projects that have either replaced (GradebookNG) or intended to replace them (Bullhorns) in core.
I believe that Gradebook classic will just be stealthed still for 12 because the performance issues may not be resolved.