First of all - yes they're "just tools" and that's pretty much what I said - Go is for servers and it won't "rule them all", and I wouldn't write the obvious if it weren't for the massive Go hype.

Another angle though - a language comes at a massive cost of vocabulary (builtins and libraries) which dwarfs the cost of learning a new grammar (easy compared to natural languages though a cost in itself). A language suited for a narrow niche will still replicate a lot of libraries, tools etc. Whoever pays the costs, too many languages in one's toolbox, be it a person, a company or society as a whole, is not necessarily a net gain.

So if Java could have gotten goroutines without having to make a whole new language... would Go be a good idea? (I don't know the answer and maybe it's practically irrelevant but it's an interesting question I think.)