We've built our own protobuf library called Polyglot, which encodes messages in an order based on their types rather than the number associated with the proto3 file. Because of this, we don't currently support backwards and forwards compatibility the way gRPC does.
=== Performance comparison with C++ arena allocations TL;DR - We don't have specific benchmarks for this (yet).
C++ arena memory allocations are similar to Go's memory pools in the way they try to pre-allocate and reuse memory. fRPC is written in Go, but it doesn't currently use memory pools. Adding support for them is on the roadmap, though! that's a future optimisation that we expect will provide even further performance optimisations.
As far as C++ goes, though, the library is currently written in Go and we don't have a C++ version on the roadmap. That said, this is brand new and we're absolutely listening to determine if it makes sense to implement fRPC in other languages, such as C++ and Rust.