Could the Advanced Grading method somehow implement an LTI interface? I'm wondering if, for example, it could be used to pass submitted documents to a service like Turnitin or an ePortfolio system like Chalk & Wire. The service would facilitate grading by the instructor, then pass back the result.
This would allow the LTI-compliant grading tool to be "bolted on" to any Activity type that supports Advanced Grading. It would also allow existing defined Assignment activities to be converted to Turnitin or whatever without having to be completely rewritten.