I imagine it's supposed to be similar to how Apple's iAd platform works for iOS apps. It's a bad shake for third-party ad networks, but it's great for user privacy, since third-party origin requests are no longer being made to anyone but the platform owner (who then anonymizes the impression metrics they give back to the ad creators, who just have to trust the platform-owner's stats.)
That's not true. There is space in amp for a variety of iframe'd ad providers.
Wouldn't that effectively mean that in a search query followed by an AMP site visit only Google has the opportunity to show targeted ads ?