Years ago I flew on Tower Air. Tower Air contracted their security through El-Air, as such they were ahead of where we are today. But one thing I always griped about was this policy being useless.
You see I had borrowed an old laptop (and I mean super old, where only the front half flipped up with a screen). The PC still worked, but the battery was long dead. So when they required me to turn on this ancient behemoth, we spent the next 20 minutes trying to find a plug so I could boot it. As soon as they saw it begin it's boot sequence, they gave me the okay. A lot of PITA for little benefit IMHO.
Why do I say this?
If anyone intended to build a bee oh em bee inside a laptop or cell phone. Why wouldn't you just take advantage of all the existing software and circuitry? It is a lot easier to just set a timer, use a program like Automate It, or even write your own basic Android app to control any such set up. A simple Bluetooth trigger and you can remotely detonate either an internal or external explosive trigger.
So in no way do I see requiring proof that a device turns on as adding anything to our security. Rather, it merely means all those people laid over for 4 extra hours and now with a dead battery on their iPhones will have to hand over their phones to TSA. (Who will make a LOT of money selling used iPhones until they get sued for having sold devices with personal data - after which they will just destroy them.)
Luckily, many Android users will simply keep a spare TSA battery on hand. And smart vendors will set up stands that sell "pre-charged" USB battery packs for $150/each right outside the security lines.