[mattiemass]

(author of that quoted blog post here). You are correct, there's nothing new about apps offering plugins/extension systems. What's new here is: this works across sandboxed apps, support for remote (out-of-process) views, and the extension permission and discovery system is entirely managed by Apple.

[duped]

Like I mentioned in another comment most of this has been practice for awhile. The big one is discovery, but there have been techniques to fix that (like standard install locations). AU (v2, v3) is a good example.