Right? This feels like an "arms race" similar to scraping vs. anti-scraping; countermeasures will be developed, likely due to the action of actors entirely disconnected from what you're doing, but to block something else in the ecosystem... and you'll need to re-engineer your approach entirely. Rinse and repeat.
(The amount of innovation in anti-anti-scraping that's resulted from "sneaker bots" - automated scalping of limited-edition shoe releases - is astounding, and somewhat relevant here in how an environment can become adversarial in ways that impact broad ecosystems. I suppose the equivalent here would be environmental ads that seek to penetrate noise-cancellation in a similar way.)
I suppose, though, that all this is good news for a company that wants to turn your bicycle bell into a subscription product!
I don't see why this would become an "arms race." There's no particular competitive value in filtering out this ONE sound.