I had a lot of hope for crdt as a more general technique for client server communication, but it seems that usage of crdt for anything other that collaborative documents is pretty rare
I think CRDTs can be applied to more than just documents, and they can for sure be applied to client-server communication, and peer-to-peer for that matter.
I used CRDT to create a collaborative graph tool using the 2P2P-Graph. There is a pretty good Wikipedia page about CRDTs, which I recommend you read. It can definitely be applied to many use cases were the datatypes such as counters, sets, maps, sequences, etc are used.
CRDTs allow multiple concurrent mutations to the same data. If it's just between a single client and server then there's no need for this. There are some databases that are now using it for replication though.