It was resolved as it is a duplicate of http://jira.jboss.com/jira/browse/RF-6
However, RF-6 is still there.
This is not trivial task. To implement database sorting we need to have query data model, - instead of abstract data model, we must have something that understand database, which is a bit outside of the JSF scope.
We are trying to do something in our upcoming rich:scrollableGrid, where we have sortableColumn.
However, it is much simpler to find specific solution on the application level. Just use a4j:commandLink on the column header and pass column name as a parameter.