Habe gerade bei Chris Take was interessantes gesehen.

public class GenericEventArg<T> : EventArgs
{
   public GenericEventArg(T value)
   {
     Value = value;
   }   public T Value { get; set; }
}

public event EventHandler<GenericEventArg<MyClass>> MyClassEvent;
public event EventHandler<GenericEventArg<List<string>>> StringListEvent;
public event EventHandler<GenericEventArg<int>> IntEvent;