On their page about AMP Viewer Google admits that they are collecting user's data when they view AMP pages [1]:
> The Google AMP Viewer is a hybrid environment where you can collect data about the user. Data collection by Google is governed by Google’s privacy policy.
With replaced URL it will be more difficult to spot.
Now, they want to remove the remaining user interface element that says they’re spying on me!
Also, this makes it even harder to ad block their junk at the network layer (is foo.com down, or is this more amp bs?)