On the subject of automatic PA's
Consider
Does the aircraft have the capability in it's PA system to play pre-recorded messages?
If so
Pre-recording one isn't a problem
Triggering it is solvable
Turning the PA volume up automatically could be difficult
Would the Pax actually listen to it??
Should all airlines be made to cover the costs of all of the above for, what is after all, not a common occurence? Which in the first scenario could mean having to replace airframes!
Don't forget there was a thread in Pprune a few weeks ago complaining when an auto "prepare to ditch" messge was inadvertedly manually triggered.