I'd say it's far better strategically to make sure swift on iOS is the official mainstream way of developping an app ( which isn't the case yet) before you start to advocate using it on a totally new territory.

How much credibility would you have if you were to say to backend developpers " swift is such a great language, you'll love coding with it on the server side", and they hear that iOS still can't include the stdlib because the language is still not stable enough ? I've tried, and the answer is none.