Hi friends,
The problem with that is that the spy should have access to the end market a priori.
So the use of this technologies can be done in a very limited way.
The problem with this kind of trojen horses is that you have to have physical access to the hardware infrastructure at design time and that's not always possible.
That's why soft trojans are more effective. They run on standard hardware and are installed/activated remotely.
I'm not telling that HW trojans are useless. I'm just saying that their use is much more limited and the "niche" is very small.
By the way, hardware trojans exist for a while now. and many technologies contained them and still contain them