[mercurial]

> That sounds like a "no true scotsman" argument.

I don't see how this is a "no true scotsman". Maybe a non-true "no true scotsman"?

> If comments were added to the spec then normal tools would support them just fine.

Plain comments, sure. Comments with custom annotations in them, not so much.

> Besides, JSON has already become a common format for config files. Config files that don't allow comments are truly a step backward.

Maybe this wasn't such a good idea in the first place?

[MichaelGG]

How not? Comments with annotations would be ignored, just like a special annotation key. Either way, you'd end up with a parsed document that isn't what the original creator intended.