Yes, I'm looking forward to ES6. And I agree that Node's strength is that Javascript is truly the lingua franca of the modern web, which I why I would even bother using it.
But the value of running everywhere is also why ES6 is not a panacea. As you say, soon we won't need promises "on the server". But I want my codebase to run correctly everywhere. Promises are a bandaid that I'll need for quite a while yet.