Yes, it'd be really nice to see this in the standard go tool though. I'm not sure why they bother with installers on Mac OS for example, and it'd be much nicer just to call the go command to update the go system too and switch between versions as well (particularly if you want to test against several versions at once).
They do almost offer this for betas, you can do:
go get golang.org/x/build/version/go1.8beta2go1.8beta2 download