Predicted IFSD rates are not expected to rise because of ash ingestion as it would only be an minute contribution among all the various causes.
Futhermore ETOPS is predicated on independendant en-route failures and not on common cause which affects more than twin engine aircraft.
The safety related effects of ash are developed in minutes and immediately obvious (cabin lights go out etc.). The longer term effects are discernible over many flights as deteoration of performance and addressed by maintainence between flights.
I can't understand why posters are making this doom and gloom stuff up rather than leaving it to operators and OEMs to sort out.