My company has cleared me to refactor & open-source (MIT) an AngularJS+D3+PHP dashboard tool I wrote (similar to Chart.io, but intended for integration with existing admins/backends).
My fear is, despite the PHP backend simply being a connector for various data sources, the audience for this project would be apprehensive towards contribution or usage because of PHP's stigma.
I can fairly easily convert the backend code to use Node instead, but would only want to do so if it helped get more eyes on the project and improved chances that others could help me with contributions.
Don't change the language of your project just because of popularity. Use node, python, ruby only if the end result will be a significantly better then the current is. When I say significantly I mean compared to the time you will spend to convert it.
In terms, of end users, those that will actually use the dashboard. They don't care what language you use.