Thank you for your feature request.
It is already logged in our ToDo list for new features, but its implementation will be very hard because the editor uses two different IFRAME elements in Design and Html mode and to make the implementation cross browser and bug free this will require a serious time of investigation and testing. It will also decrease the editing performance when loading a large content in the editor. That is why this feature is not logged with high priority and I cannot provide a firm estimate when it will be implemented.
Nevertheless, I agree with you that this is a very nice and user friendly feature and it will definitely increase the usability of the control.
All the best,
the Telerik team