I think from the context it's pretty clear that "hack" in this case is referring to "being forced to unlock". Yes, they could still deliberately break encryption for future OSes and phones, but the same could be said of any software, open or closed source.
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?
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?