Multiple Storyboard Animations for Same Property
Don't see where multiple storyboard animations targeting the same property should actually pose a coding issue for .NET. Initially it might seem like the developer shouldn't be allowed, but that's not really true provide the BeginTime and Duration properties keep the setting of the same property by two different animations separated from each other. Just remove the code check that throws the exception when two animations target the same property. If they do target overlapped in time, declare that as "undefined as to what will happen" and leave it to the developer to make the time sequence correct.