You're not going to get much processing out of anything at ~50nm in size. In this case there is a claim that a chip has been inserted and while it's small, it's going to be nowhere near ~50nm.
I am dubious mostly because of the speed and heat issues - in order to intercept and modify what is effectively cross bus information on the fly the intercepting chip needs to be rather fast otherwise the communication between components will be unreliable and a fast processing chip tends to generate heat. Put a generator of heat inbetween the substrates of a board and you're asking for (thermal) trouble.
Not impossible, of course, but rather unlikely. It's much more likely that a chip is inserted just on the board itself because this is going to be somewhat easier to achieve. Or alternatively to just modify the software that is on these devices in the first place - no physical trace at all then.