We are going to remove the obsolete tag from OptionType property and obsolete just some of the values in its enum type (OptionListType). This will enable you to use it with None and CheckList options as before.
We obsoleted the property in order to remove the OptionList support for RadTreeView. OptionList was indicated as barely used by our clients and brings quite a bulky and complicated code inside the control. Also it is one of the stoppers for future refactoring and optimization of CheckList functionality.
Having in mind your feedback we will bring back the property and obsolete some of its accepted values. The change should be present in our internal build next Monday.
Hope this helps. Please let us know if you face other issues regarding OptionType property.
the Telerik team