A better solution is to use YAML for things like configuration files. It's more pleasant for a human than JSON would be even if it supported comments, and there are nice parsing libraries available for every popular language.
Ultimately, it makes JSON unsuitable for configuration files (there are other reasons for that, to be fair, like over-verboseness)
Also, I hope, trailing commas and binary types.
As for adding comments to the spec--again, the idea is to prevent shadow information showing up that isn't obvious to a conformant parser.
If you give people the ability to smuggle data in comments, that's exactly what they'll do. At least this way people know that what they're doing isn't "to spec" and that their sneaky parsers are not following the rules.
The reasoning is also incredibly short-sighted.
This is probably going to sound like asking someone to catch sunlight in a teacup, but wouldn't it have been more productive to stress the importance of syntax adherence and consistency rather than remove it altogether? There's really nothing stopping someone from abusing the rest of JSON for silly things so leaving comments out seems a bit redundant.
