This document is about the use of languages within the project itself.
Fuchsia, as a fundamental principle, supports "bring your own runtime" -- if you are a PIE ELF executable and can dynamically link against libzircon.so (the syscall ABI) and speak the platform's RPC protocols, you are a Fuchsia app.
The Fuchsia IDL compiler is designed to support third party backends for other languages beyond the core platform languages.
I've moved on to other things, but I'd be very surprised to learn this had changed.
> This document is about the use of languages within the project itself.
Only in part; they also specifically mention whether or not they will support use of each language by end-developers. (As you say, end-developers can use whatever they want, as long as their language has a C-ABI FFI, but that's not the same as being "supported".)
Fuchsia, as a fundamental principle, supports "bring your own runtime" -- if you are a PIE ELF executable and can dynamically link against libzircon.so (the syscall ABI) and speak the platform's RPC protocols, you are a Fuchsia app.
The Fuchsia IDL compiler is designed to support third party backends for other languages beyond the core platform languages.
I've moved on to other things, but I'd be very surprised to learn this had changed.