Apple may have inadvertently erased doubts that Siri would come to the Mac. Brian Roemmele has discovered that asking iOS' Siri the right question (such as "open settings in the window") sometimes produces a response saying that the voice assistant can't find the Finder app -- you know, a crucial part of the Mac's interface. Barring the inclusion of a full-on file manager in iOS 10 (not very likely), this hints that Apple is laying the groundwork for Siri in OS X.
We wouldn't count on the feature being finished any time soon. Apple historically releases new OS X versions in the fall, so you may have to wait a while if you're not the experimental sort. However, the apparent slip supports rumors that Apple would talk about Siri for the Mac at WWDC -- don't be shocked if there's a beta (public or otherwise) with voice commands in the near future.