Where is the minefield? In accepting things that are not JSON, such as trailing commas and comments? That's silly. Everything blue and yellow in that matrix is

Where is the minefield? In accepting things that are not JSON, such as trailing commas and comments? That's silly. Everything blue and yellow in that matrix is entirely OK and should be green ("undefined" means "anything goes", and the spec specifically allows accepting more than JSON, so "should have failed" is bogus). That leaves a few parser bugs in form of orange and red, but they're corner cases (like surrogate pairs or 10000 nested arrays) and fixable.