There is no doubt in our minds that Siri will eventually become a part of Mac OS. We just don’t know when. Some reports speculate that it may happen with OS X 10.9, which is rumored to be announced soon.
If Apple follows its current trend, it should be announced sometime this month with a WWDC ’13 in-depth reveal, and a release about a month or two later.
The speculation comes from some job postings at Apple. They are looking for a Siri UI engineer, and it seems that there is a lot of work to do. Apple likens it to creating an operating system within an operating system:
This is a broad-ranging task – we take every application that Siri interacts with, distill it down to fundamentals, and implement that application’s UI in a theme fitting with Siri. Consider it an entire miniature OS within the OS, and you get a good idea of the scope!
Of course, each of these little “snippets” corresponds to an individual application, so you will have extensive cross-functional work with many other teams. You’ll need to work with them to enable access to their data and behaviors, and wire them up to your implementations. As a result, strong API design is needed to keep communications ideal.
It’s also very possible that Apple just wants to expand Siri for now. That said, the company has been working to bring iOS and OS X into a more unified environment. This is definitely another step in that direction.