I am currently creating a navigation controller for an iOS mockup and have setup a symbol for this.
I would like to be able to use my symbol and then adjust properties from the property inspector, for example (Title Text, Back Button Text). Even better would be able to add additional UI widgets to the nav bar.
Note: I am not looking for a navigation controller template, this is purely an example of how this kind of new functionality could be used. The key point is that there would be a way to:
1 - Create property items for any self created (custom) symbol.
2 - Choose what this property item links to within the custom symbol.
3 - Set values for these at mockup design time.
I believe a similar request was raised near the end of last year (2015) I thought I might attempt to be a bit more specific regarding the use case.