I'm not sure if you're being sarcastic, but for parallel construction they'd still need to find this exploit. Are you saying Google Project Zero is out there to hide the traces of backdoors?
It doesn’t seem all that unrealistic. These companies buy and research every single bug they can get for iOS and eventually you have enough that you can glue them together in to full exploits. When you have enough funding, this stuff becomes realistic.
Never underestimate the extremes computer science types will go to in order to prove a point.
I believe this line of thought has not been given enough attention recently.