I just lifted the restriction, but it doesn't change anything because of this code in GenericHistoryView:

IStructuredSelection structSelection = (IStructuredSelection) selection;
//Always take the first element - this is not intended to work with multiple selection
//Also, hang on to this selection for future use in case the history view is not visible
lastSelectedElement = structSelection.getFirstElement();

In other words: we never get more than a single element into the view anyway.