The big question is how hard it is to fake up some stickers that will to fool casual inspection. The visual part is no problem, especially for the silver stickers. The obvious problem is the serial numbers. If the serial number of each sticker is recorded (and checked!) then it becomes impractical to just make up a bunch of stickers at home and replace whatever sticker you destroy. I wonder how the security people inspect them and how often.
One thing I noticed is that the blue stickers are basically unreadable without a flashlight, which is probably considered a feature (it's hard to replicated) but means that inspection is slower and easier to bungle. In any case, even if serial numbers are checked you might be able to use a label printer to print new serial numbers onto premade stickers once you know the serial number of the sticker you want to replace. Of course, if you're targeting a specific plane you can figure out what the serial numbers are on one flight and then replace on the next. This sounds like a lot of work, though, especially since there are other places to hide stuff on an aircraft (or in the airport).
Second, what happens if one of the seals is broken? For the system to be of use, this must trigger some kind of inspection. If the inspection is cheap, that's no big deal. But if it's onerous, then tampering with a few seals would force the airlines and TSA to incur a pretty substantial expense (and potentially delay).
Finally, it's not clear what threat is being defended against. Remember that people are generally not searched entering the plane, so it's easy to just hide your weapon (or whatever) in the airport somewhere (inside security) and then carry it on the plane in your bag. Is there some obvious advantage to hiding contraband on the plane proper that I'm overlooking?
I think there is an advantage to hiding contraband on the plane instead of in the airport, but such a minor one that it's probably not really worth the effort to stop. Say you have one person in your terrorist group who has basically unfettered access to a plane through being, say, a maintenance worker. He hides a weapon on a plane and leaves it. The plane takes off and lands at some other city. An accomplice gets on board the plane at that point, gets the weapon, and uses it.
Investigators will most likely assume the weapon came through the security checkpoint at the airport the accomplice originated, not the one the plane originally came from. Thus, you can help protect a valuable asset (your guy with the access) from discovery.
Rather contrived, I suppose.