Even if this is not the current ulterior motive and the reason is really a terror threat, this will eventually happen. It's just all to convenient if a foreign diplomat or businessman is coming to your country to take out the laptop and quickly insert a firmware backdoor.

Why would we expect a country that bugged the German Chancellor or provided malware that was inserted by another five-eyes partner into the telephone system that the EU administration used, not to (ab)use this opportunity?

Once this is in effect, don't travel to the US with a laptop.