In reply to Otto.

That's indeed the key Otto, not allowing lock-in features to creep into themes. Ironically WooThemes (now an Automattic acquisition) were one of the worst in the day (we know first hand as we offered WooThemes as an option with our Typepad to Wordpress migrations).

The big push now at Wordpress.org to insist that advanced functionality go into a plugin and not the theme is an important step towards data portability for Wordpress publishers.