> If I were Evil-Tim-Cook, I'd have a deal with the FBI (and other agencies) where I'd hand over some user's data, in return for them keeping that secret and occasionally very publicly taking Apple to court demanding they expose a specific user and intentionally losing - to bolster Apple's privacy reputation.

The FBI wants its investigations to go to court and lead to convictions. Any evidence gained in this way would be exposed as coming form Apple; notwithstanding parallel construction:

* https://en.wikipedia.org/wiki/Parallel_construction

As for other agencies, I'm sure many have exploits to attack these devices and get spyware on them, and so may not need Apple's assistance.

I imagine if you have the information parallel construction becomes trivial.