We are targeting the ASP.NET platform and RadEditor is an ASP.NET AJAX control, which depends on server-side creation. It is not possible to dynamically create RadEditor client-side, because the editor depends on a number of resources like links, colors, etc which are configured on the server as well as the editor's scripts are embedded in the Telerik.Web.UI.dll.
When the cloneNode(true); is executed then only the editor's HTML is cloned but not the editor's object and for that reason the editor is not editable and it cannot be made editable.
For that reason our recommendation is to choose another approach to multiple the editor on the server.
the Telerik team