This cute legal theory hasn't been tested at web scale to my knowledge (closing down shop due to threat of lawsuit != the theory is tested, just that the depth of someone's wallet has been tested and found wanting).
What makes it curious in the web context is the following: say we can decompose the transmitted web page into the "content" and the "ads".
It is occasionally the case that the full ad content is directly embedded in the transmitted work but that is not the norm; far-and-away the most typical setup is:
- the content is transmitted as part of the page
- the ads are transmitted as scripts embedded in the page; the ads are thus not directly transmitted but if the receiving user's browser operates in a particular fashion than those scripts will execute and insert the actual ad-content into the page in a way the user can see it
If an ad-blocker works by stripping out javascript there is a smidgen of a derivative-work argument here.
If, instead, the ad-blocker works by altering the operation of the javascript interpreter (eg: leaving it unable to connect to the ad server) then nothing in the combined content+ads has been changed by the ad blocker.
If the ad-creating javascript were somehow involved in protecting the content (eg: the web page is transmitted "encrypted"; the page's javascript is waiting for a key to be transmitted in the ad content before decrypting the page content) then you might be able to work up a DMCA anti-circumvention claim, but your user experience would be so terrible it probably wouldn't make economic sense to do this.
All that said: an "ad-blocker" program is safe so long as it has substantial non-infringing uses.
Given the vast range of computers in use (in terms of cpu/ram/intended usage/etc) and given the vast range of hazards out on the internet (phishers/virii/etc.) a program that facilitates one or both of:
- "hostfile management" (blocking or restricting address to particular servers or ip ranges, etc.)
- "javascript management", adding additional checks or safety controls to how a browser interprets javascript
...is clearly going to have substantial non-infringing uses and should have a clean legal bill of health provided it is marketed as a generic security / performance solution and not an "ad-blocker".
Thus in the unlikely event that your legal theory vis-a-vis ad blocking is found to have teeth all that will be needed to continue ad blocking as before will be to rebrand the software as a more generic hostfile+javascript management with a way of sharing and importing configuration files from other users (allowing the users, then, to block ads themselves).
So as cute as it is this isn't a theory that will do much more than prevent any serious commercial ad-blocking venture from getting serious traction.