On Upgrade #78: Rename Everything, Myke Hurley and Jason Snell discussed why Apple is finally adding Siri to the Mac. They aren't sure Siri will be useful on a Mac.
I completely agree that Siri will be less useful on Mac than on iOS, tvOS and watchOS. My office is an open space and talking to my computer would be less than ideal.* It might be a little more useful at home when I'm not worried about disturbing people around me.
I could envision sitting down at my (always listening) Mac and saying "Hey Siri. Log me in." And then through some combination of confirming the presence of my iPhone (or Apple Watch) and voice identification, the computer magically logs me in to my account like Touch ID on iOS. I think it should be reasonably secure and would be a nice feature.
I'd also love to be able to trigger simple one word commands like "mute" and "pause."
I really do hope Apple has a creative approach in the works and not just a rehash of what is on their other devices. I've really been impressed with the way Siri works on Apple TV and hope they bring that level of implementation to the Mac.**
* Translation: Annoying for those around me.
** Or is it macOS?