From alisoncc, above:
I do not believe that there is adequate science available to accurately predict damage for every flight undertaken.
It appears to be WORSE than that. Not only is there no accurate PREDICTION. The suggested methods (starting with visual examination post-flight) have already been demonstrated to be insufficient to cover all situations where turbine damage has already occurred. Instrument and engine data recording during flight are also not (it seems) a reliable indication of ash damage.
I've suggested already that filters on heat-exchangers etc. fed via compressor bleeds will contain an accurate record of whatever has passed through the turbine and therefore should be a primary focus of post-flight checks but no-one else seems to consider this important. (Having looked at the recent CAA FOD on the subject of ash, I'm not reassured that bases are covered by the suggested procedures.)
At best, I predict that operators are in for a torrid time covering wildly escalating turbine maintenance costs, quite apart from the downtime waiting for non-available spares.