Justin Tadlock is building a repository that will contain examples of using the Customize API for advanced things. He explains:
The goal is to provide examples so that theme authors are not bypassing the core API and doing weird things like injecting links into the DOM via JavaScript, which can and will most likely break in future iterations of the customizer in core WordPress.
His first example is on how to properly show a link in the customizer for a theme upsell.
