You mean doubleclick.net? Alas, that's a typo that would let the ads in.
Like you I redirect doubleclick and "many others". But not to localhost. I like to log all the requests either via pflog or a socket logger. Useful for examining what apps are trying to do from my device over the network. Sometimes I redirect certain domains to my own httpd and serve my own "fake" resources (placeholders for in-app ads, etc.).
You say "any network I'm in charge of".
What if there were a DNS caching server reachable from anywhere that blocked these ad servers for you? That is, what if there was a "public DNS" like 8.8.8.8 or 208.67.222.222 except not run by a company that sells ads or "security services"?
What if there was a turnkey ad-blocking DNS caching server solution that one could run on any suitable hosting provider virtual machine instance?
Would anyone be interested in such a thing? I have had this personal DNS idea for many years, ad blocking is becoming much more popular only recently.
I think users controlling their own DNS is a key step toward taking back the www from the "corporate dreck". Maybe blocking ads is the stimulus for such a change.