I read in a pommie paper years ago that in most B737/A320 size jets there's an average of 12 - 15 cellphones switched on every flight anyway, either forgotten about in luggage, or pax just ignoring the rules.
Every man and his dog and his 2-year-old kid has an ipad AND a smartphone these days - plus all the new gadgetry like bluetooth music headsets - it's only getting worse so, trying to come down on the pax harder and harder to switch all their gear off is like plugging the hole in the dike with your fingers. If there is or was a safety risk, then putting that safety onus on the pax to do the right thing, has never worked and it never will.
This policy change was inevitable sooner or later, if the FAA has done their research and says it's ok, then I'm comfortable with it