[jitl]

there are a zillion of these "json pro" kind of things: superjson, devalue, capnweb, all with slightly different ideas about how to lower high-level semantics to json's available types. it's so easy to do this kind of thing, its a real https://xkcd.com/927/ situation.

CBOR (Concise Binary Object Representation) has JSON-like semantics with type extension support; with built in type extensions its much easier to get some agreement about registering certain magic type IDs to mean certain things. for example from a random google search for "cbor datetime" https://j-richter.github.io/CBOR/date.html; there's an IANA registry of type IDs: https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml

however, it is binary.