I think it will be that nice ST2 would allow comment lines inside any of the JSON config file. It would be great for documentation and easier to maintain.
I believe it does... there are comments in the default sublime-settings.If you change e.g. the font size or color scheme using the menus, though, Sublime Text will rewrite your user settings file and delete all comments.
Ah, you are right, it does supports '//' comment line! Thanks for pointing it out.