While we have an UploadWizardUploadInterface class, its utility is somewhat questionable, given that we still have myriad selectors for known elements strewn around the code.
Ideally it would be commonplace to save an interface DOM element (or more appropriately jQuery object) to an object when you create it, for example, this.interface.details.$titleField is a lot simpler than $j( '#title_' + id ), and way more readable. And it makes it easier to extend the project - once T51989 is fixed, we'll have sound documentation on all the available interface objects as well.