Yesterday at SMX West, Behshad Behzadi of Google said Google is indeed working on bringing voice search capabilities to shopping. He said Google is working on "conversational search," such as being in a store and looking at products and saying "I want to buy X cheaper" or "what shops are near me?"
Behshad Behzadi is not on the ad side, so I don't think he was talking about product listing ads. Although, PLAs do have a lot of structured data that would easily allow one to buy directly via Google Voice search through voice commands only.
For example, one can say:
... show me blue t-shirts
... I like the one from target
... buy that one in large
And then the transaction is done and the shipping details goes to his Google Now.
I can see that happening fairly soon.
Here are some tweets on that topic from the show:
Google working on conversational shopping #smx— Barry Schwartz (@rustybrick) March 1, 2016
Forum discussion at Twitter.