Many experts have expressed the concern that moving more and more OTC trades to a CCP is exchanging a lot of small risk for a few very large risks. A standardized stress test could be a good instrument, but does one size fit all? The other question will be if its really possible to design a standardized test. Obviously Moody's, being a rating agency, feels a rating is the way to go.
Moody's has written a proposal and is asking for feedback. The actual proposal can be found here, free registration is required. The proposed rating uses four different categories: Intrinsic Credit Strength, Operating Environment, Qualitative Adjustments, and Affiliate and Systemic Support. The proposed rating is a scorecard showing an overall assessment and a breakdown by category.
If rating is the way to go or not is up in the air, one thing is sure: the discussion not likely to go away any time soon.