It seems a pain in the @rse but seeing as tablets laptops etc have to go in their own 'tray' at the security point anyway all we have to do is switch them on beforehand, no big deal for PPRuNe ers I would think, and perhaps big signs before entering the security area for the general public.
The problem is this. Many people don't have these devices already turned on, and it may take up to a minute to boot-up a device. Couple that with the person having multiple devices and the waiting time at the X-ray belt will quickly become astronomic. Just think of all the delays we have right now because the %&$#!! in front of you has not already extracted their liquids bag and removed their honking huge belt buckle, bangle bracelets, etc. before reaching the belt. Add to that the additional delays of waiting for multiple devices to power up, and it becomes a CF.