They changed their add-on API and are in the process of deprecating the older one which allowed for radical UI changes. That's probably what he was talking about.
Nope, it just that older extensions will and IIRC the developer of the tree-style-tabs extension was really vocal about the fact that he disliked the new API. He had claimed it would be impossible to port his extension to the new system. I'm not clear on the history of it all, so I don't know if it was possible at the time or not.
They changed their add-on API and are in the process of deprecating the older one which allowed for radical UI changes. That's probably what he was talking about.