Just a clarifying question to understand if I understand librdx correctly, it seems you've implemented a language explicitly for being easy to be used as CRDTs for syncing purposes (with specific types/structures for communicating just changes too?), rather than taking an existing language and then layering that stuff on top?
It depends on what you mean by a language. If JSON then yes. There are ways to implement CRDT by layering on top of JSON (see Automerge) but the result is really far from idiomatic readable JSON people expect to see.
RDX is more like CRDT JSON DOM in fact, not just JSON+. If that makes sense.