In reply to Ahmad Awais.

@mark-k: We actually work very hard to engineer new capabilities in the customizer so that they can be extended and we try to document these in Make/Core posts and demonstrate them via feature plugins. As a developer myself, I'm personally more interested in making the customizer a good experience for developers (for myself even) to extend rather than creating new user features. I want to create a foundation to facilitate future improvements. For example the changeset improvements took 2 years of iterating and prototyping, but in the 4.7 release there's not really a flashy user feature that it brings. Nevertheless, it will open doors for new user features in subsequent releases and it improves the architectural foundation for the customizer to add those features and for plugin authors to develop extensions.

As for WPSE, I've answered questions before on the customizer, and just this week I made a point to subscribe to a daily digest of the theme-customizer tag. A question was asked today in fact and already got a good answer, which I see you found: http://wordpress.stackexchange.com/a/247247/8521

So I'll get notified of your question once you post it there. Cheers.