There is another possibility; EU countries may decide that this amounts to tacit admission by Google that the revenue generating event in ad sales happens on the browser, and ad revenue is therefore always taxable in the country where the browser (and viewer) are located. No more laundering international revenue through tax havens.
And since Google just demonstrated such an effective verification mechanism ... well they can just repurpose it to track all such taxable revenue for the countries in question ... otherwise they might be deemed a criminal enterprise and have to be blocked nation-wide.
No need to block the useful parts, just the illegal tax-evading ad empire.
... and countries can move fast when there is a lot of money to be had ...