(Speculation) I'd guess this is so they don't have to solve the hard problem of allowing arbitrary prompts and distinguishing between them (and QC thereof).
This way Apple only need to add a few new prompts like "send a message with $appname to $person", and ensure they work consistently.
If so, and if security is the cause: on Android, apps have the option of looking up the app triggering an intent of theirs to check its APK signature in order to verify the origin (allows for secure inter-app communication).
I would assume it is all. But limited to the few example categories of queries the demonstrated.
Interestingly, they did not demonstrate a media query (i.e. Play Metallica on Spotify). If they don't open up for that, it is a pretty significant limitation of the API.
Add SiriKit support only if your app implements one of the following types of services:
https://developer.apple.com/library/prerelease/content/docum...