Fact as reported: Flight crew did not hit the ditch switch.
Fact as reported: FA did not know they were ditching until they were on the water.
Could be addressed in training if the investigation deems it worthwhile.
More generally the learnings from this accident are IMO that passenger evacuation procedures never play out exactly as designed because, generally, no passenger has previous training or experience. I.e. there will always be those people going the wrong way and who do not listen to or react to commands from anyone. The challenge when designing future emergency procedures is to be able to handle also these "disturbances" and still ensure everyone survives.
It will be interesting to hear how real accident experts will judge the outcome of this emergency situation. Obviously it's an excellent benchmark of an accident where everyone survived despite some, let's say minor, imperfections in the execution of the evacuation procedures. The next challenge will be to see what can be done to achieve the same survivability also in more challenging external circumstances than was the case on the Hudson river.