First we ought to recognize that if there is a war to be fought there never should have been one in the first place.
Formats can co-exist and complement each other - look to the example of RDF a format that leverages the things it needs from XML (types and namespaces) while doing the job it was designed for better than XML.
Secondly this war is not being waged on technical grounds because the notion that one should attempt any non-trivial system development effort built on a format that does not have a subtyping capability is risible.
JSON folks waged a very effective PR campaign, XML folks sat back and barely answered and the appeal of the loudest voices held sway. You can't stem or reverse that tide with arguments rooted in technical merit.
Let's take a realistic example - an air traffic control data exchange.
There is a common core concept of an Airport but it could be a local or international, public or private and then there would be variations on how different countries model one.
IOW there is a core Airport that has been modelled with subtypes of LocalAirport, USAirport, NZAirport, PublicAirport, PrivateAirport.
Somebody comes along and wants to remodel this in JSON and the reason when you've cut through all the is that bullshit JSON has eaten XML's lunch and if you disagree that it would be bullshit let's just agree that it's not going to be because you can do the subtyping in the data model you originally designed in JSON.
So my attitude is let them make that argument and if they win the contract let them go build the system.
