1) the author does not mention in his example the use of timezone offsets (which are a part of RFC3339), that's a bit irritating
2) Timestamp parsing and emitting sucks, no matter the language, because the format specifiers are wildly inconsistent across platforms. I prefer the good old UNIX timestamp, because with it there's no complex massaging needed in order to operate with the timestamp.
Also, the author is missing comments entirely - no matter if shorthand // or long-form /* */ gets included, JSON desperately needs commenting ability; but on the other hand I'm worried about compatibility with older systems...