Commas aren't a huge deal for me personally but if there were to be a "json2", dealing with them and removing the double-quoting requirement for keys would make authoring a little easier. Ultimately these are issues that are easily solved with a linter though.
A standard date type would be huge however, and I'll add to that built-in support for comments. These two things would expand the scope of what you could do with JSON. JSON is already used in so many places for config files but without comments it can be a poor choice.