For scenarios requiring a constant exchange of information, such as streaming data or real-time updates. After the initial handshake, data is exchanged directly over the connection with minimal overhead. Lower latency is especially beneficial for high-frequency message exchanges. Gaming, live auctions, or real-time dashboards are well suited. I also think that real time collaboration is under-explored.

JSON-RPC is request-response only; the server cannot send unsolicited messages. gRPC supports bidirectional streaming, but I understand that setting it up is more complex than WebSockets.

I will concede that horizontal scaling of RPC is easier because there's no connection overhead.

Ultimately, it really depends on what you're trying to build. I also don't underestimate the cultural aspect; fair or not, JSON-RPC feels very "enterprise microservices" to me. If you think in schemas, RPC might be a good fit.