I don't think they have the balls to pull something like that.

If a manager suggest this in a meeting, the legal folks will eat him alive. If it comes from higher upps, then someone will leak this and that will be the end of Google.

More likely it will get annonomised and feed into since ML. But it would be super illegal to do what you're describing and with as many employees as Google has someone would notice and leak that.

Why would they blatantly violate the law for legal reasons?

You guys will never be happy. Yet you will not apply the same argument to any other product by any other company.

Time for a GDPR information request to find out...

I think so, too. I imagine it's the same with opting-out of "Location History" - you opt-out of seeing the log, not out of locations actually being logged.

It would be cool if there were a way for Google to prove (maybe cryptographically?) the absence of some data on their servers, so that I could verify that my location data has actually been deleted.