Hello Jon ,
I have talked to the team but they were pessimistic about the future of such feature. The general opinion is such problem should be solved at the data layer level rather than at the UI. I believe the approach with custom collection or an intermediate proxy collection is as close as we can get.
I am not sure about the practical purpose of such setup , but I may recommend to use an observable collection as source for RadDataForm. This way you can listen to the collection changed events of this collection and manage your original collection. In other words what you delete form the observable collection bound to the RadDataForm will not be deleted from the original collection.
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>