I don't think acting like an open ecosystem is the be-all and end-all of security is productive. Most organizations (let alone individuals) don't have the resources to vet every line in every piece of software they run. Software follows economies of scale, and for hard problems (IE, TLS, font rendering, etc) will only have one or two major offerings. How hard would it be to introduce another heartbleed into one of those?
As someone who has done quite a bit of reverse engineering work, I have no idea how I'd identify and isolate a vulnerability found by fuzzing without the ability to even look at the machine code.
For the same reason I do not independently vet every line of source code I run, but still reasonably trust my system magnitudes more than anyone could - and I argue, nobody can - trust proprietary systems. And that is because while I personally may not take initiative to inspect my sources, I know many other people will, and that if I were suspicious of anything I could investigate.
Bugs like Heartbleed just demonstrated... well, several things:
1. Software written in C is often incredibly unsafe and dangerous, even when you think you know what you are doing. 2. Implementing hard problems is not the whole story, because you also need people who comprehend said problems, the sources implementing them, and have reason to do so in the first place.
Which I guess relates back to C in many ways.
I look forward to Crypto implemented in Rust and other memory / concurrency / resource safe languages. There is always a surface vector of a mistake being made that can compromise any level of security - if you move the complexity into the programming language the burden falls on your compiler. But in the same way you can only trust auditable in production heavily used sources, nothing is going to be more heavily used and scrutinized, at least by those interested, than languages themselves.
The important thing about the secure enclave thing is that it pushes security over the line so that the attacker has to comprimise you befor you do whatever it is that will get you on somebodys shitlist.
Locking themselves out of the Secure Enclave isn't anywhere near sufficient. As long as the device software and trust mechanisms are totally opaque and centrally controlled by Apple, the whole thing is just a facade. There's almost nothing Apple can't push to the phone, and the audibility of the device is steadily trending towards "none at all".
If the NSA pulls a Room 641A, we'd never know. If Apple management turns evil, again, we'll never know. If a foreign state use some crazy tempest attack to acquire Apple's signing keys ... again, we'll never know.