It seems like they're just trying to remove any distinction between 1st and 3rd party cookies at all.
Non-goals: ... Information exchange between unrelated sites for ad targeting or conversion measurement.
To get something onto the list (https://github.com/GoogleChrome/first-party-sets/blob/main/f..., currently empty) you need to make a public PR with rationale (https://github.com/GoogleChrome/first-party-sets/blob/main/F...). It doesn't look to me like DoubleClick would qualify?
Quite literally the same company is trying to neuter adblocking with Manifest V3 right now and pitched it as "improvements to security."
Google’s changes only affect people who use vanilla Chrome. And the people who use vanilla Chrome without any privacy extensions don’t have much privacy to begin with, so First Party Sets does not make things much worse than they already are.
If all you want to do is blocking cookies, why would you use a browser extension for that? Most browsers ship with a configuration option to disable them.
For Chrome/Chromium it's over at chrome://settings/cookies
To avoid breaking sites that cease to function without cookies. EFF's Privacy Badger is pretty good at this and it allows you to select individual domains in the popup to add or remove the ability to receive cookies.
DoubleClick is hard coded into every Chrome browser :) [1]
[1] https://chromium.googlesource.com/chromium/src/+/e51dcb0c148...