My point is that it'll be worked around by blockers, which means they'll then implement more robust methods (which as a side-effect might break accessibility, see how Facebook splits the "sponsored" subtitle in lots of spans) and so on and so forth.

Instead, the ads should be done in such a way that most people don't have any incentive in blocking them (I personally would like to see ads provided that 1) they are vetted and 2) they are for products I'm interested in, based on the choices I make in my profile). Given that, the few outliers that would still end up blocking them wouldn't be a problem worth solving (you can always offer a paid tier to remove ads for the people that truly don't want any ads).