This is a good analysis of how Apple might implement a Siri API. I have some points I'd like to add too, based on my own (cursory) research into this topic.

First of all, I feel confident that whatever API Apple exposes will probably resemble one of the existing APIs we've seen before, such as:

- Window/Kinect's Speech API[1]- I have no experience with this one, but one of my friends used it a few years ago and described it as "loading grammars for Kinect to use in parsing speech".
- The HTML5 Web Speech API[2] - I prefer the version exposed by Annyang.js[3] which is geared towards creating "event handlers" that fire when a certain command is spoken. The Web Speech API gives you no access to how the audio is parsed into words, however the implementation in Chrome is actually pretty awesome at detecting proper nouns, place names and the like.
- The Alexa Skills Kit[4] - This example is interesting because Alexa is essentially an "OS-level" assistant who has to support all the services that have been registered to Amazon.

I'd also like to point out some of Apple's philosophy (as well as some of their already completed work on Siri) and how it might influence a Siri API:

- Starting in iOS 8, Apple gave Developers the ability to create "extensions". "Siri Abilities" would probably be manifest as an extension, and would follow the lead of existing extensions in terms of limitations. This means users would have to opt-in to your app's Siri abilities, and the option will not be super obvious to them unless they wanted to look for it.
- In an interview on John Gruber's The Talk Show[5], Eddy Cue talked about how Siri for TvOS has to be able to distinguish when Spanish speakers are throwing an English movie title into the middle of a sentence. My guess is that their speech parsing logic is super complicated, and they won't give 3rd party developers a hook into it.
- Apple doesn't like to build things that require tons of configuration. They probably won't give users the ability to configure which app should answer "Send a message to mom". This would mean having a screen that listed every command Siri supports. Even if it only listed the commands that had "conflicts", listing out all of Siri's abilities to anyone (even just developers in a piece of documentation) is something Apple will never do.
- Apple's gotten better about this over the years, but they still tend to make choices that privilege their apps over 3rd party apps (even if it's just a side effect of a bigger policy).

So where does that leave us? I think Apple's Siri API will most closely resemble the Alexa Skills Kit.

Developers will have to register a "namespace" for their app. The "namespace registry" will be like the URL protocols mentioned in TFA. Developers will to scramble to register their name, as it'll be what users have to say to indicator which service Siri should use to fulfill the request. Once inside a namespace, developers would have total freedom to write any commands they want.

In the end, I predict that Siri commands (if used with the wake word) will sound like this: "[Hey Siri], tell [WhatsApp] to send a message to [Mom] that says [I'll be home for Thanksgiving]." Not the "Tea, Earl Grey, Hot"-est thing in the world, but still really useful! (And this would be feature parity with Amazon Echo)

If Apple sees the above command as too awkward or cumbersome, I predict that they will not release a Siri API. I can't imagine them releasing an API that gives developers more control. I do think TFA is right though about "Voice Search in Apps" being a possible halfway point.

[1] https://msdn.microsoft.com/en-us/library/jj131034.aspx

[2] https://www.google.com/intl/en/chrome/demos/speech.html

[3] https://www.talater.com/annyang/

[4] https://github.com/amzn/alexa-skills-kit-js

[5] http://daringfireball.net/thetalkshow/2016/02/12/ep-146