...I've previously used 'control' classes to allow non technical users to configure form validation parameters in an external XML file, however the form & model still required development time.
As an extension of the form class to function more like a SkinnableDataComponent the form items become 'ItemRenderers' containing typical inputs. Bi-directional binding is maintained by introducing a DynamicModel class which is also capable of tracking dirtied fields & performing validation.