Which should remind companies releasing similar products in the future that it's cheaper to design them with built-in privacy features rather than patch them as an afterthought.

You're absolutely right.

That said, I think companies also have to consider the saleability of privacy features. How many Echos would you, personally, buy if they had a mechanical switch? How many people do you think would make the same decision? How does this stack up against the change in failure rates from a physical switch?

Again, you're completely correct. It's cheaper to design in privacy features up front. I can see some wrinkles that make the question more subtle, though.