Re: The queues will get horrendous
I'm already on the NSA list for reading the reg, so I'm not bothered about confessing all here, but I travel to the US regularly with a laptop, spare laptop battery (not all aircraft have in seat power), external HDD, tablet, various plugs (some aircraft do have in seat power), bluetooth headset, usb keys, micro-sd cards in my phone, etc., etc. I try not to check bags so everything has to be in hand luggage. I've never once been asked to power anything on.
The most examination I had was my electronics got swabbed for ion detection of explosives. That's by far a better way to test stuff going through than just powering it on, as the chances of you fitting explosives into your electronics without getting any on the outside is very slim. As previously noted, if everyone has to prove it by powering on, we'll all be standing in line for a very long time...