I don’t buy it. Siri will just say “let me book you an Uber” like it does now; or “let me order that book for you on Amazon” like it does now. Last I checked, a driver can’t get into a personal B2B relationship with Siri. That does mean the user might spend less time in the app… but that engagement is still measurable. Orders are engagement.
What if I just say "get me a car" and it decides whether to use Uber or Lyft based on availability?