The ISO format can be used for a lot of things which your JSON format could never be used for. ISO works great in file names, for example. And it's really nice

The ISO format can be used for a lot of things which your JSON format could never be used for. ISO works great in file names, for example. And it's really nice in some circumstances (such as the file names case) that alphabetical sort is identical to chronological sort. And just... why would you spend 10x the space to represent timestamps when ISO timestamps (or, well, RFC 3339) works just fine?