Unfortunately they aren't. But those are all worked on by people with academic (or equivalent) PL backgrounds whose hand-waving I trust much more. Also don't forget the existence of GHC's core, and Rust's Mir (OCaml I'd hope have a good well-defined core language). Basically, for human purposes, there is a spectrum of "quasi-formality" and Go is not winning.
So, basically, you're criticizing Go for something that even languages like Haskell, OCaml and Rust, worked on by people with academic PL backgrounds, don't do.
Having a well-defined core language like GHC's Core or Rust's MIR doesn't give your a proper formalisation. It just makes the formalisation easier by reducing the scope of the language. Even ECMAScript 6 "desugars" to a core language. It doesn't make the language more formalised.
The fact is that none of Go, Rust, OCaml and Haskell are "properly formalised", as of 2016. Nobody wins here.
Finally, get very excited for http://plv.mpi-sws.org/rustbelt/ .