I recently came across a case involving (among other things) a professional malpractice claim against an auto loan servicer. The court held that loan servicers are not in the category of professions that are subject to a professional malpractice claim under New York law. Presumably this would apply to mortgage loan servicers as well.
This is relevant not just to RMBS litigations but to any of your investments in mortgages (or other assets that must be serviced).