I would like to access multiple realtime databases within the same firebase app project.
As you can find in the documentation "Scale with Multiple Databases > Connect your app to multiple database instances":

// Get the default database instance for an app
var database = firebase.database();

// Get a secondary database instance by URL
var database = firebase.database('https://testapp-1234.firebaseio.com/');

Would be nice, to have this in angularfire2 too.