The terms of the settlement don't say anything about "forcing" Y to do anything. Basically all we get is a 2.5 year period from which to make claims instead of 90 days. Everything else is just promises to make a few changes in the way they detect invalid clicks.
Those of us who have already been submitting invalid click reports get nothing.
And you don't need to do anything to become part of the "class" ... there really is no class. All Y advertisers have the opportunity to go through their logs for the past 2.5 years and submit suspect entries to Y for resolution. That's it. That's all there is. If Y tells you that they are valid clicks, you're done. You have no more recourse.
The mailer they are sending out (got one a couple of days ago) is simply an opportunity for anyone receiving it to GIVE UP THEIR RIGHTS to make any sort of claim in the future and in any future lawsuits. That's all the mailer is good for: To inform you of how you can give up your rights to future actions.
Looks like Google should have gotten Y's lawyers ...