I think JSON was circa 2006, but why pick on Maven when you could pick on NIEM, FPML or any other non-trivial data interchange standard.
XML being "dead" has alot to do with cloud vendors refusing to support it in their offerings because cloud native and cloud migration is the flavor du jour.
Which mean somebody at Google and AWS sat down, surveyed the enterprise landscape and decided organizations using XML shouldn't have a place in the cloud to put their data, simultaneously those enterprises haven't connected the dots and told them there ought to be a place where we can put our data because we are paying for this shit.
Was that a commercially driven decision or one driven by a few overly influential engineers.
Does everybody who has XML data really want to have to convert it to JSON in order to be cloud native, or is there a latent opportunity for an enterprising vendor with an eye for a gift horse.