Maybe other languages will allow you to program more efficiently, but they have a learning curve and a fraction of the developer adoption that nodejs has.
When you pass your project onto someone else, there's a high chance they are already familiar with nodejs. Whereas if you pass a project to someone else in a less-known language, they are likely not familiar with it and will need to overcome a steep learning curve.
If you want maintainable projects, where a freelancer is always available who knows how to continue development of your project, then go with nodejs. If you want to learn a new language or framework, do it for pet projects with no collaborators.
Since it is a side project, you can swap out Ember and try Elm.