It's silly to not write your software to handle every possible input instead of every input you think is likely based on some predictions about humans. Failure to do that is why YAML is so broken.
JSON isn't a format conducive to handwriting even if it probably should have made more accomodations for that at the start. Right now it can't even handle trailing newlines. But if you want to fix that, call it something different (maybe even JSON2), for heaven's sake.
I doubt anyone would handwrite an entire gigabyte JSON document, but they might hand-edit a machine-generated one to make a change someplace in it, end up putting in a trailing comma, and have the document pass their local tests but crash a remote parser.
