The Index method in the TMVCJSONRPCController has a try/except code block that handles all Exception types.
This means that an application writer is prevented from writing a high level exception handling block that allows custom exception handling as in the normal RESTful mvc application, because all custom error classes are descendants of Exception so get caught.
For instance It prevents an application from being able to log nested exceptions, and also log the call stack using 3rd party code such as Eurekalog.

Issue #191 added a custom exception handler to address this issue for RESTful applications.
I propose a similar pattern for JSONRPC, which would be called from the exception block on the TMVCJSONRPCController.Index method.
Useful objects to pass through are:

• the Exception object
• the JSON error response, so the application writer can add to the message or change the error code.
• the original WebContext, to provide access to request properties
• and optionally a boolean variable "ExceptionHandled" set to true, which stops the error from propogating, or could be set to false to reraise the exception.
  Thoughts ?