Dr. Farmwald has the credentials to testify as an expert, and IMO the failure of RMBS is completely irrelevant, and possibly not even admissible.
However, I question how influential (or at least how dispositive) expert testimony is in any event. Maybe it is necessary to have it, particularly when your opponent presents expert testimony. However, it seems to me that the question of patent validity ultimately is a legal question, and in my experience, you have to tread very carefully when you present expert testimony on a legal conclusion as the judges tend to have a notion that issuing legal judgments is a province in which they the judges are particularly qualified (as well as anointed to do so).
I'll be happy to be corrected by a patent litigator on these views.
Thanks.