May 1748, Surrey, England.
William Thomas Json: One last touch and my magnum opus will be complete...
Me, appearing in a portal of light: Stop! I come from the future, no time to explain, you MUST allow trailing commas, or the world will suffer!
Json: Sorry, no can do, I just sent the specification off to the printers. Maybe next format, thanks!
Me, disappearing in a flash of sparks: NOOOOOOOO!!!!