Hi John,
There are many aspects to why this is almost impossible to implement.
On the server, a control is a logical unit, on the client - it is a collection of HTML elements and javascript, subject to browser rules and limitations. These two entities are completely different. Yes, you can render a control (e.g the editor can trick it to render its HTML), but then you will probably expect that to change properties of that control or for the control to be both editable as well as to behave as if it is in a non-editable environment.
Once issues of this kind start being taken into consideration, it becomes clear why there is no such commercial implementation available on the web. Many frameworks and CMS systems exist that aim at addressing such a task, and they do so in a manner than a WYSIWYG web-based editor can do things.
Best regards,
Tervel
the Telerik team