No, not all browsers, and not all of ISO 8601. Safari only added ISO 8601 Zulu parsing in the last few months, and IE only at version 9. Neither support explicit timezones yet. Which means there's still a large population of browsers that will choke. As I said, date parsing is a mess.
In any case, my general point still stands: dates are the only "data" type (i.e. not a function, regex, etc.) which is not supported by JSON. So even if there were a usable universal serialization format, you'd still need to post-process the results of the JSON parser to convert the strings into dates.
In any case, my general point still stands: dates are the only "data" type (i.e. not a function, regex, etc.) which is not supported by JSON. So even if there were a usable universal serialization format, you'd still need to post-process the results of the JSON parser to convert the strings into dates.