It might be indirect enough to be considered no effect. Perhaps the scope of these env vars are vars that can modify cmd/go behavior only after the Go tree has been installed, and cmd/go tests are out of scope. I wasn't sure from the documentation, which is in large part what this issue is about.
Hmm, that's an interesting question. The main purpose of cfg.KnownEnv is to control which variables may be stored (and read) from the go/env configuration file, but today we do not read GOROOT_FINAL from that file: