Ashley
One of my main use cases for the Addon SDK, is portability and reuse of code. everything is packaged together nicely. a lot of things that can be done with JS is much more convenient to move to addon.
And I think that stems from JS and event not having good interoperability.
If I had some code I wanted to reuse across projects, I need to import the js file, then create functions in the event sheet to act as like some middle layer to properly invoke my JS code from the event sheet.
setting up triggers or event from JS code to the event sheet is also pretty tedious.
As where with the Addon SDK I can package all these things up nicely with a little bit extra boilerplate. but then my code is portable, and it's exposed in the scripting interface. triggers are easy. and even thought that is a bit more work the experience is much more seamless, and much more reusable.
Maybe I am thinking about the SDK incorrectly, because while it can be used to integrate Third party services, I think the main use case is adding extra functionality in the engine.