Earlier quoted context omitted.
what's the best modern alternative that is designed in this way?
gRPC ticks most of the checkboxes. Unfortunately these are lessons that have to be learned over and over. Anything based on JSON is generally suspect. If you see the terms "quick" or "simple" in some marketing splash-page, assume the author has not thought about the hard problems like security and long-term interoperability. Similarly, if you find yourself hand-rolling RPC client code and calling methods on something…
huh :) ! gRPC is a 'r-p-c' framework, and uses protobuf for serialization. you should be comparing protobuf to cap'nproto.