Hand-editing JSON may not be the most important way of interacting with it...
In that case, the arguments in favor of breaking long-established compatibility for the sake of hand-editing should be particularly strong.
If personal forgetfulness about editing around commas or date strings are strong arguments, then they should surely also apply to every programming language that uses commas or lacks the concept of a date literal. After all, the code of programming languages exists to be edited, and JSON is merely a means of serialization.