I do not think the NTSB is going to let this accident slide through the cracks without testing injestion abilities on turbines that are long in the tooth compared to a fresh engine
Well this can open up a can of worms. It is a known fact that the engines are at least as good as the test engine when they come out of the shop. After that it's a case of how much wear. Nobody can dial in all the variables involved with an ingestion so the idea is to make the single demonstration test strong enough to get you through what mother nature deals up most of the time.
You can draw lines in the sand all you want but in the end they will be blown away by the next day when you leave them out in the open.
About all the NTSB can do as an investigating agency (not a regulator) is ask questions about the specific engines installed vs their maintenance history and manufacturers recommendations. They can have an analysis performed to show just how much operating margin was available at the time of the incident and then review this against published standards, AD's etc.
It there is a question about ingestion adequacy it needs to be asked against the acceptable regulatory standard at the time or against service history over time.