I’m glad that opting out is available, but there is no practical, technical enforcement.
What sort of technologically-enforced mechanism might you envision that does not rely on legal enforcement?
Lately I practice the only tech-enforced option I know of: wholly pull the plug on wi-fi. Indeed, this means I only have ethernet in my house and wifi radios are disabled. It also means for my smartphone to reach the cloud, I am reverse tethering over USB. Try getting a crowd of people to do that. I will praise you if you can get 10 people to do that.
There is such a thing as bluetooth routers. So a middle ground would be to pull the plug on wi-fi and use bluetooth instead. Though it’s a compromise because we cannot¹ be certain that Google does not also harvest bluetooth. But at least the limited range would mean fewer cases where the signal reaches the street. Of course you would have to be okay with the slower speed.
If Google violates their own policy, it’s legally actionable. So if you are going to run wi-fi you can do your part in helping grow the legal liability that Google has signed up for. I see no good excuse for not appending _nomap to the end of your SSID. It’s just pure lazyness not to.
¹ well strictly speaking, we might know from the location data whether Google uses bluetooth. But if it’s not part of the location data it would not be an absolute indicator that it’s not collected.