Let me jump into this forum thread. My name is Stefan Dobrev and I'm the author of the RadExpressionEditor component and the expression engine behind it. You are absolutely right that the component lacks documentation and more user case scenario examples. We are sorry for this and will try to improve this one step at at time for the future.
Now onto your questions. Currently the expression engine supports only plain old CLR properties (including indexers as well). It does not support dynamic objects (via IDynamicMetaObjectProvider), nor DataTables /DataViews/ICustomTypeDescirptor. The underlying extensibility points are there, but we did not have enough resources to implement it for all scenarios. We will do this eventually in some of our next releases.
Until then I can suggest you to look at MicroModels framework for possible way to handle objects of dynamic shape. You can also look at Vladimir's lightweight DataTable (which also generates on the fly
CLR types with properties). Both solutions are for Silverlight, but can be compiled for WPF as well. Alternatively you can take a look into the Automapper framework for a general purpose solution.
Hope this helps,
the Telerik team