one big difference between email and the systems that the author suggests is that email is a standard and a protocol, where the systems referenced by the author are pretty much single implementation systems maintained by a single authority.

some of these authorities have all sorts of structure to prevent corruption. passionate people, nonprofit or open governance. however, they are still single points of failure, or targets, or whatever you'd like to call them.

it seems that after years of pain with poor effectiveness of specification or poor verification tools for implementations, it has become en vogue for modern cryptosystems to insist on tight centralized control of reference implementations to ensure correctness. (otherwise known as the apple computer model). while this does seem to work in terms of ensuring high quality and problem free implementations, it does open up the single point of failure issue.

i'd argue that email's replacement must retain email's greatest quality: it's an open specification, not a system or implementation owned or controlled by a single entity and that the true challenge in bringing it to fruition won't be clever protocol and cryptographic design (although these will be crucial) but also substantial advances in protocol definition and implementation verification such that any competent developer can implement compatible components and plug them in.