I mean the way it was shown is that WebBundles allow the author of that content to arbitrary hide and package content in such a way where you cannot filter specific content; so either you view a page with ads and trackers or you don't see anything at all.
The infrastructure needed to randomize and remap URLs for bundles is basically the same as for endpoint URLs. You can already serve all requested content, including things a blocker might want to block, as first party, meaningless URLs. https://my-site.com/1g276dn4kas for everything. Store the URL map in the session data rather than bundle.
I don't even think the hard part in either case is mapping the URLs and serving the content, but rewriting all the references to the URLs in the source files.
(Disclosure: I also work for Google)