Does nothing for publishers' needs for deeper control and analytics. Just a "feel good" gesture that results in additional complexity for everyone involved. Google is not the only company in the world that knows how to load a page efficiently.
The publisher's cookie-based analytics will operate on the origin in the URL bar in this case. The document (though not the delivery server) will have access to publisher origin cookies.
Conceptually, you can think of a signed exchange as a 301 redirect to a new URL which has already been cached by the browser (so there is no 2nd network event). The cache was populated by the contents of the signed exchange, assuming the signature validates.
