I still think there's a need for standardized APIs in this situation. At some point, the context constraints mentioned in the blog post have to get translated into some action with parameters. I'm guessing that action will be API calls to other Google products behind the Duplex Google Assistant UX.
"Ok Google, can you reschedule my Dr. Appointment this Friday for next week? I have a conflict." -> calls the Dr and reschedules -> adapts result to rebooking action with partners (ie, an api call to your Google calendar) -> applies action and responds to you.
There is still quite a bit missing from this to be a useful AI product. It's getting really close though. I can't wait until this makes it into Google Assistant and it can call a restaurant to ask about gluten free options while I'm driving.