The queues will get horrendous
If they demand that every electronic item is powered up.
Where will they put all the people with laptops who carry a portable HDD with them while they get all the cables out and plug everything together?
What about all those USB Keys? They are electronic devices
The same goes for SD cards etc.
This is all a total waste of time. That spare bay (or even a Cd/DVD drive bay) in the laptop could contain a 'device'. The goons at Security won't know the details of each laptop and what it might contain in every nook and cranny.
In the 1980's this was tried at Geneva airport. It didn't last very long (AFAIK).