What about this?
- Host content A subject to copyright on site X
- Devise platform Y on site Z whose claimed role is to check whether user has rights to access content A
- Send DMCA on any list or apparatus that tries to block site Z on the ground that it would be a circumvention attempt of platform Y to unlawfully access content A
- Piggy-back on platform Y to do some tracking/stat building about ad-blocking
- Manically laugh at your brilliant scheme
Note that content A and site X could literally be anything and anywhere, possibly even as trivial as a haiku such as "our hard work / by these words guarded / please don't steal". It doesn't even matter that no one is ever meant to ever see the copyrighted work. In this case the copyrighted work could very well be the text/image displayed when ad-blocking is detected, making A == Y and Z == X to confuse everyone while they think this is about displaying ads W.
To sum it up: ad blocking enabled -> copyrighted work displayed -> user views content unlawfully -> ad blocker just circumvented a technological restriction intended to prevent this -> DMCA applies.
Another possibility is that platform Y is preventing ads W to be shown to a certain theoretical group G of people, hence if you are blocking Y, control about W cannot be enforced, whether you were part of group G or not (and of course you were not, but then even though you're not infringing on copyright about seeing W, you're still infringing on circumvention of a device intended to control copyright of W).
Totally roundabout, entirely bogus, but hey, not the first time such heavily pictured crap could still hold water in court.